STEAM  BOILEKS 


McGraw-Hill  BookGompany 


Electrical  World         The  Engineering  andMining  Journal 
En5ineering  Record  Engineering  News 

Railway  Age  Gazette     .  American  Machinist 

Signal  Engineer  American  Engineer 

Electric  Railway  Journal  Coal  Age 

Metallurgical  and  Chem  ical  Engineering  P  o  we  r 


ENGINEERING  EDUCATION  SERIES 


STEAM  BOILERS 


PREPARED  IN  THE 

EXTENSION  DIVISION  OP 
THE  UNIVERSITY  OF  WISCONSIN 


BY 
E.   M.   SHEALY 

ASSISTANT    PROFESSOR  OF  STEAM  ENGINEERING 
THE     UNIVERSITY   OF  WISCONSIN 


FIRST  EDITION 


McGRAW-HILL   BOOK   COMPANY 

239  WEST  39TH  STREET,  NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.  G. 

1912 


COPYRIGHT,  1912,  BY  THE 
McGRAW-HiLL  BOOK  COMPANY 


THE. MAPLE . PRESS. YORK. PA 


PREFACE 

This  book  has  been  written  out  of  the  experience  of  corre- 
spondence teaching  in  this  subject  in  the  Extension  Division  of 
The  University  of  Wisconsin.  It  is  the  result  of  well-matured 
plans  to  produce  a  suitable  text  for  instruction  by  mail  as  de- 
veloped through  actual  experience.  The  work,  therefore,  was 
written  primarily  for  correspondence  students,  and  is  intended 
for  the  use  of  firemen  and  others  who  may  be  in  responsible 
charge  of  boiler  rooms. 

In  order  to  best  fulfill  the  main  purpose  of  this  instruction, 
the  operation  of  boilers,  rather  than  their  design,  is  treated  in 
considerable  detail.  Much  descriptive  matter  relating  to  boilers 
and  boiler-room  equipment  is  included  because  it  is  realized  that 
many  firemen  are  familiar  with  only  the  particular  equipment 
which  they  happen  to  be  using,  and  wish  to  know  something 
of  other  types  of  equipment. 

On  account  of  the  increasing  importance  of  efficient  combustion 
of  fuels  and  of  the  attention  now  being  given  to  smoke  prevention, 
these  subjects  are  treated  in  detail.  The  chapters  on  "Chem- 
istry of  Combustion"  and  "Fuels"  form  a  basis  for  the  study 
of  the  proper  burning  of  fuels.  Following  these  are  chapters 
on  "Firing"  and  "Smokeless  Combustion  of  Coal."  These 
chapters  treat  of  the  best  methods  of  using  fuel,  and  also  of 
different  forms  of  furnaces  and  apparatus  for  securing  smokeless 
combustion,  and  of  different  forms  of  mechanical  stokers. 

The  chapter  on  "Smokeless  Combustion  of  Coal"  was  com- 
piled by  Mr.  E.  B.  Norris,  Associate  Professor  of  Mechanical 
Engineering  in  the  Extension  Division  of  The  University  of 
Wisconsin.  The  author  desires  to  acknowledge  the  assistance 
of  Mr.  Norris  and  Mr.  H.  J.  Thorkelson,  Associate  Professor 
of  Steam  and  Gas  Engineering  in  the  College  of  Engineering  of 
The  University  of  Wisconsin,  for  their  careful  reading  of  the 
manuscript  and  for  many  valuable  suggestions  which  have  been 
utilized. 


263615 


vi  PREFACE 

The  text  is  liberally  illustrated  in  order  to  enhance  its  value 
to  those  for  whose  use  it  was  prepared.  A  number  of  manu- 
facturers furnished  cuts  of  their  apparatus  for  this  purpose  and 
their  cooperation  which,  in  some  cases,  involved  considerable 
effort  and  expense  on  their  part,  is  gratefully  acknowledged. 

E.  M.  S 
MADISON,  Wis. 
Dec.  1,  1912. 


CONTENTS 

CHAPTER  I 
TYPES  OF  BOILERS — FLUE  AND  FIRE-TUBE  BOILERS 

ARTICLE  PAGE 

1.  Boilers 1 

2.  The  shell      ,  .1 

3.  The  water  line 1 

4.  The  steam  space 1 

5.  The  disengagement  area .1 

6.  The  heating  surface 2 

7.  The  grate  surface 2 

8.  Tools 2 

9.  Classes  of  boilers 2 

10.  Cornish  boilers 4 

11.  Lancashire  boilers      (J 

12.  Galloway  boilers 7 

13.  Fire-tube  boilers 7 

14.  Portable  boilers •'•    -| n 

15.  Locomotive  boilers 14 

16.  Scotch  marine  boilers v   .........  16 

17.  Vertical  fire-tube  boilers .    -   . -j.    •  17 

CHAPTER  II 

WATER-TUBE  BOILERS 

18.  Water-tube  boilers     .    . 21 

19.  Babcock  &  Wilcox  boilers 21 

20.  Murray  water-tube  boiler 24 

21.  Edge  Moor  water-tube  boiler   . 25 

22.  Atlas  water-tube  boiler 27 

23.  Stirling  water-tube  boiler 28 

24.  Vogt  water-tube  boiler 29 

25.  Vertical  water-tube  boiler 31 

26.  Wickes  vertical  water-tube  boiler 31 

27.  Cahall  vertical  water-tube  boiler 32 

28.  Rust  vertical  water-tube  boiler 33 

29.  Comparison  of  types 35 

CHAPTER  III 
BOILER  CALCULATIONS 

30.  Boiler  horse  power 39 

31.  Heating  surface 40 

vii 


viii  TABLE  OF  CONTENTS 

ARTICLE  PAGE 

32.  Corrugated  flues. 45 

33.  Strength  of  shell v 46 

34.  Strength  of  furnace  flues 49 

35.  Riveting 50 

CHAPTER  IV 

STAYS  AND  STAYING 

36.  Principles  of  staying 55 

37.  Stay  bolts 55 

38.  Boiler  heads    ..... 58 

39.  Diagonal  stays    .    . 59 

40.  Girder  stays ........:..  60 

41.  Gusset  stays 63 

42.  Stay  tubes '.- 63 

43.  Radial  stays    ....'........ 63 

44.  Through  stays 64 

45.  Dished  heads      ........  ^.    ..... 64 

46.  Tube  setting 64 

47.  Manholes  and  handholes 68 

CHAPTER  V 
HEAT  AND  WORK 

48.  Changing  heat  into  work  ..    ^   ...............  71 

49.  Work 73 

50.  Power ".....,...    v    .    .    .    . 74 

51.  Horse  power 74 

52.  Energy .    .    .    .    ..  . 74 

53.  Heat '. 75 

54.  Energy  of  fuels 76 

55.  Sensible  and  latent  heat 76 

56.  Temperature 77 

57.  Measuring  temperatures 77 

58.  Thermometer  scales 77 

59.  Thermometers  and  pyrometers 79 

60.  The  unit  of  heat 83 

61.  Relations  of  heat  and  work      84 

62.  Heat  cycle  of  a  steam  power  plant ;  ..    ,\  .    .  84 

CHAPTER  VI 
EFFECTS  OF  HEAT 

63.  Expansion  of  solids 87 

64.  Coefficients  of  expansion 87 

65.  Expansion  of  liquids 88 


TABLE  OF  CONTENTS  ix 

ARTICLE  PAGE 

66.  Expansion  of  gases 89 

67.  Absolute  zero      90 

68.  Transmission  of  heat 91 

69.  Radiation 91 

70.  Conduction      91 

71.  Convection 92 

72.  Circulation .    .""J    .    .  93 

73.  Formation  of  steam   . 95 

74.  Disengagement  surface 96 

75.  Steam  space 96 

CHAPTER  VII 

PROPERTIES  OF  STEAM 

76.  Atmospheric  pressure 97 

77.  Barometers .  ...   .    .    ..    .  97 

78.  Gage  pressures 98 

79.  Absolute  pressure 98 

80.  Vacuum 99 

81.  Evaporation 101 

82.  Saturated  steam ,    .    .•-. 102 

83.  Steam  tables -..'". 103 

84.  Pressures 103 

85.  Temperature  of  evaporation ..-.'. ../....  104 

86.  Heat  of  the  liquid .    .    .105 

87.  Latent  heat .-,...  106 

88.  Total  heat  of  steam 107 

89.  Density  of  steam 108 

90.  Specific  volume 108 

91.  Expansion  of  water  into  steam .  108 

92.  Allowance  for  feed- water  temperature    . .  108 

93.  Interpolation  from  tables 109 

CHAPTER  VIII 
.  ACTUAL  AND  EQUIVALENT  EVAPORATION 

94.  Wet  steam 115 

95.  Quality  of  steam 117 

96.  Steam  calorimeters 118 

97.  Separating  calorimeter 118 

98.  Throttling  calorimeter 121 

99.  Superheated  steam 129 

100.  Total  heat  of  superheated  steam 129 

101.  Density  of  superheated  steam      131 

102.  Superheaters 131 

103.  The  future  of  superheated  steam 132 

104.  Equivalent  evaporation 132 


x  TABLE  OF  CONTENTS 

ARTICLE  PAGE 

105.  Factor  of  evaporation 134 

106.  Boiler  horse  power 136 

CHAPTER  IX 

FUELS 

107.  Classification  of  fuels 137 

108.  Wood 137 

109.  Peat 137 

110.  Coal 138 

111.  Lignite 140 

112.  Bituminous  coal 141 

113.  Caking  coal 141 

114.  Non-caking  coal 141 

115.  Cannel  coal      .    .    .    ...    ,v  .    .: 141 

116.  Semi-bituminous  coals 141 

117.  Semi-anthracite 142 

118.  Anthracite 142 

119.  Petroleum 142 

120.  Heating  value  of  fuels 143 

CHAPTER  X 
CHEMISTRY  OF  COMBUSTION 

121.  Combustion 147 

122.  Oxygen    .    .    .    . 147 

123.  Carbon 148 

124.  Chemical  definitions 148 

125.  Molecules  and  atoms 148 

126.  Atomic  weights 149 

127.  Molecular  weights 149 

128.  Compounds  of  carbon  and  oxygen 150 

129.  Process  of  combustion  of  fuel 151 

130.  Air  required  for  combustion 152 

131.  Flue  gas   : 155 

132.  Flue  gas  analysis 157 

133.  Preparation  of  reagents 160 

CHAPTER  XI 
METHODS  OF  FIRING 

134.  Methods  of  firing 161 

135.  The  coking  method 161 

138.  The  alternate  method 162 

137.  Spreading  method      163 

138.  Rules  for  hand  firing 163 


TABLE  OF  CONTENTS  xi 

ARTICLE  PAGE 

139.  Smoke  prevention 165 

140.  Mechanical  stokers 165 

141.  The  Wilkinson  stoker 166 

142.  The  Roney  stoker 187 

143.  The  Murphy  stoker 168 

144.  The  Jones  underfeed  stoker ,    .    .    .  170 

145.  The  Taylor  gravity  underfeed  stoker 172 

146.  Chain  grates 174 

147.  Advantages  and  disadvantages  of  stokers      175 

148.  Oil  burning "...  176 

CHAPTER  XII 

.     THE  SMOKELESS  COMBUSTION  OF  COAL 

149.  The  smoke  problem 179 

150.  Principles  of  smokeless  combustion 180 

151.  Causes  of  smoke 182 

152.  Means  of  prevention .  183 

153.  Types  of  furnaces 188 

154.  Chain  grates    .    .    .' '  .    .  ..    .    .  189 

155.  Inclined  grate  with  front  feed 189 

156.  Side  feed  stokers 190 

157.  Underfeed  stokers 190 

158.  Hand-fired  furnaces .  190 

CHAPTER  XIII 

SETTINGS 

159.  Foundations 195 

160.  Setting  for  fire-tube  boiler 195 

161.  Boiler  supports 201 

162.  Bridge  wall 202 

183.  Dutch  ovens 203 

164.  The  Chicago  setting 204 

165.  The  Burke  furnace 206 

166.  Back  connections 207 

167.  Blow-off  connection '....'.  208 

168.  Buck  stays 211 

169.  Water-tube  boiler  settings ..211 

170.  The  Kent  wing  wall  setting 213 

171.  The  Wooley  smokeless  setting 215 

172.  Steel  settings 215 

173.  Shaking  grates 215 

174.  Grates 216 

CHAPTER  XIV 
PIPING  AND  BOILER  FITTINGS 

175.  Kinds  of  pipe 219 


xii  TABLE  OF  CONTENTS 

ARTICLE  PAGE 

176.  Determining  the  sizes  of  pipes 221 

177.  Expansion 223 

178.  Erecting  pipes 225 

179.  Pipe  covering 228 

180.  Boiler  fittings 231 

181.  Safety  valves 232 

182.  Steam  gages 236 

183.  Water  gages 237 

184.  Gage  cocks • 239 

185.  Water  columns -.    .    .  239 

186.  Safety  plugs 240 

187.  Surface  and  bottom  blow-offs 240 

CHAPTER  XV 

BOILER  ACCESSORIES 

188.  Dry  pipes 243 

189.  Superheaters 245 

190.  Foster  superheater 247 

191.  Babcock  &  Wilcox  superheater 248 

192.  Stirling  superheater 251 

193.  Heine  superheater      252 

194.  Schmidt  superheater 253 

195.  Damper  regulators 255 

196.  Feed  pumps     . 256 

197.  Duplex  pumps 259 

198.  Injectors 267 

CHAPTER  XVI 
CHIMNEYS  AND  DRAFT 

199.  Draft 271 

200.  Chimneys  for  oil  fuel. 275 

201.  Steel  chimneys 275 

202.  Concrete  chimneys 277 

203.  Brick  chimneys 277 

204.  Artificial  draft    . 279 

205.  Steam  jets 279 

206.  Mechanical  draft 280 

207.  Forced  draft 281 

208.  Induced  draft 282 

209.  Economizers  and  air  heaters 284 

CHAPTER  XVII 

BOILER  FEED  WATERS 

210.  Scale 287 

211.  Impurities  in  feed  waters 288 


TABLE  OF  CONTENTS  xiii 

ARTICLE  PAGE 

212.  The  carbonates 288 

213.  The  sulphates 289 

214.  Chlorides 290 

215.  Effects  of  impurities 290 

216.  Mud 291 

217.  Preventing  scale 291 

218.  Foaming  and  priming 291 

219.  Corrosion :.    .....  293 

220.  Treatment  of  feed  waters 295 

221.  Boiler  cleaning .    .  297 

CHAPTER  XVIII 
FEED  WATER  HEATERS 

222.  Feed-water  heating 303 

223.  Methods  of  heating  feed  water 303 

224.  Economizers ........'...  303 

225.  Exhaust  steam  heaters ,    ........  304 

226.  Open  heaters 306 

227.  Temperature  of  feed  water 312 

228.  Closed  heaters v    .    .    .    v  .    .    •  V  .    .  312 

229.  Steam-tube  heaters ',....  313 

230.  Water-tube  heaters 315 

231.  Live-steam  heaters 317 

CHAPTER  XIX 
INSPECTION  AND  CARE  OF  BOILERS 

232.  Defects  in  boilers 319 

233.  Grooving 320 

234.  Patches 321 

235.  Lap  fractures 323 

236.  Screwed  stay  repairs      323 

237.  Hammer  test 324 

238.  Hydraulic  test    . 324 

239.  Defective  fittings 325 

240.  Care  of  boilers 326 

241.  Safety  valves '  .    .    326 

242.  Pressure  gage 327 

243.  Water  level     . 327 

244.  Dampers 327 

245.  Feed  pump  or  injector 327 

246.  Low  water 327 

247.  Incrustation  and  corrosion ;    .    .    .    328 

248.  Galvanic  action 328 

249.  Blisters,  cracks,  and  burnt  plates    .    .    .' 328 

250.  Fusible  plugs       328 

251.  Covering 328 


xiv  TABLE  OF  CONTENTS 

ARTICLE  PAGE 

252.  Green  walls 328 

253.  Cutting  boiler  into  steam  main 329 

254.  Starting  the  engine 329 

255.  Firing 329 

256.  Banking  fires 330 

257.  Rapid  firing .330 

258.  Feeding 330 

259.  Foaming 330 

260.  Blowing  out 330 

261.  Feed-water  heating 331 

262.  Cleaning 331 

263.  Leaks  in  brick-work 331 

264.  Moisture 331 

265.  Disuse  of  boilers 331 

CHAPTER  XX 
BOILER  TESTING 

266.  Object  of  tests 333 

267.  Method  of  testing  boilers 333 

268.  Observations  .    .    .    .  ..    .    .    .    . 334 

269.  Weighing  the  coal 334 

270.  Sampling  the  coal  ....... 334 

271.  Weighing  water 335 

272.  Ash V. 336 

273.  Starting  and  stopping  the  test     .    .    ...    ...    .•  .,• 336 

274.  Standard  method .• .  336 

275.  Alternate  method ......./......  337 

276.  Results .    .    . 337 

277.  Calculation  of  results .  * 340 

278.  Forms  and  data 344 

Index   .  .  351 


LIST  OF  TABLES 

PAGE 

Boiler  tubes 42 

Chemical  elements 149 

Coefficients  of  expansion 87 

Factors  of  evaporation 135 

Heat  units  in  superheated  steam 130 

Materials  required  for  boiler  settings 200 

Proportions  of  riveted  joints 48 

Relative  heat  conductivities 91 

Size  and  capacity  of  boiler  feed  pumps 266 

Standard  boiler  measurements 43 

Standard  pipe  dimensions 220 

Tests  of  pipe  coverings 231 


STEAM  BOILERS 

CHAPTER  I 
TYPES  OF  BOILERS— FLUE  AND  FIRE-TUBE  BOILERS 

1.  Boilers. — A  Steam  Boiler  is  a  closed  vessel  in  which  water 
is  boiled   and  steam  formed  for  power  or  heating  purposes. 
Boilers  intended  for  power  purposes  are  made  of  plates  of  rolled 
steel,  riveted  together,  and  of  steel  or  wrought-iron  tubes.     Steel 
is  a  most  desirable  material  for  boilers  as  it  is  strong,  cheap, 
and  easily  worked.     Cast  iron  is  used  extensively  for  the  con- 
struction of  house-heating  boilers,  but  it  is  not  well  adapted  for 
power  boilers  which  carry  high  pressures.     Copper  is  also  used 
to  some  extent  for  special  kinds  of  boilers,  such  as  those  used  on 
fire  engines. 

2.  The  Shell.— The  Shell  of  a  boiler  is  the  round  or  cylindrical 
part  in  which  the  steam  is  formed  from  the  water.     The  shell  is 
only  partly  filled  with  water,  the  space  above  the  water  being 
used  as  a  storage  space  for  steam. 

3.  The  Water  Line. — The  Water  Line  in  a  boiler  is  the  height 
at  which  the  surface  of  the  water  stands.     This,  of  course,  will 
vary  somewhat,  but  should  be  kept  as  nearly  constant  as  possible. 
The  water  level  is  usually  shown  by  a  gauge  glass  which  has  the 
two  ends  connected  to  the  inside  of  the  shell.     The  upper  end  of 
the  glass  is  connected  to  the  steam  space  while  the  lower  end  is 
connected  to  the  water  space.     The  water  will  then  stand  in  the 
glass  at  the  same  level  as  in  the  shell. 

4.  The  Steam  Space. — The  Steam   Space  is  all  the  space  in 
the  boiler  above  the  water  line.     If  the  steam  space  is  too  small, 
the  violent  boiling  that  takes  place  will  cause  water  to  be  carried 
off  with  the  steam  as  it  leaves  the  boiler. 

5.  The  Disengagement  Area. — The  area  of  the  surface  of  the 
water  at  the  water  line  is  called  the  Disengagement  Area,  since 
it  is  from  this  area  that  steam  is  released  from  the  water  and  rises 
into  the  steam  space.     This  area  must  be  considered  in  designing 
a  boiler.     If  the  disengagement  area  is  small  in  proportion  to  the 
amount  of  steam  generated,  the  boiling  will  be  so  violent  over  this 

1 


2  STEAM  BOILERS 

small  surface  that  large  amounts  of  water  will  be  thrown  up  with 
the  steam  and  possibly  be  carried  off  with  the  steam  into  the 
steam  pipes.  If  the  disengagement  area  is  small  the  steam  space 
should  be  high,  in  order  that  the  moisture  thrown  up  may  be 
drained  back  before  the  steam  leaves  the  boiler. 

6.  The  Heating  Surface. — The  Heating  Surface  of  a  boiler  is 
that  surface  which  has  flames  or  hot  gases  on  one  side  and  water 
on  the  other  side.  .  It  is  by  the  amount  of  heating  surface  that 
boilers  are  generally  rated,  since  this  shows  in  a  general  way 
their  ability  to  generate  steam.     However,  all  heating  surface  is 
not  equally  effective.     The  surfaces  subjected  to  the  greatest 
heat  will  naturally  evaporate  water  at  a  greater  rate  than  those 
surfaces  more  remote  from  the  fire.     In  some  boilers,  a  part  of 
the  surface  has  hot  gases  on  one  side  and  steam  on  the  other. 
This  surface,  which  is  called  superheating  surf  ace,  is  not  considered 
as  heating  surface,  since  steam  will  not  take  the  heat  from  the 
metal   very   rapidly,    and,   therefore,   this   surface   is   not   very 
effective  in  producing  steam. 

7.  The  Grate  Surface. — By  Grate  Surface  is  meant  the  area 
of  the  grate  upon  which  the  fire  rests.     It  is  usually  expressed  in 
square  feet;  for  example,  if  a  grate  is  6  ft.  wide  and  7  ft.  deep 
the  grate  surface  is  6X7=42  sq.  ft.     The  air  openings  in  the 
grate,  through  which  the  air  passes  from  the  ash  pit  into  the  fire, 
should  be  from  30  per  cent  to  50  per  cent  of  the  total  grate  sur- 
face.    The  amount  of  grate  surface  for  a  boiler  of  a  certain  size 
depends  on  the  kind  of  fuel  to  be  burned  and  on  the  force  of  the 
draft  available. 

8.  Tools. — The  tools  used  by  a  fireman  are  a  shovel,  a  slice 
bar,  a  hoe,  a  rake,  and  a  lazy  bar.     The  slice  bar  is  a  straight 
heavy  iron  rod  pointed  at  one  end  and  having  the  other  end  bent 
in  the  form  of  a  handle.     It  is  run  under  the  fire  next  to  the 
grate  and  is  used  to  break  up  the  clinkers  and  lift  them  to  the 
top  of  the  fire,  so  they  may  be  raked  out  of  the  furnace.     The 
hoe  and  rake  should  be  of  a  heavy  and  durable  form.     They  are 
used  for  drawing  clinkers  from  the  fire  and  for  leveling  or  drawing 
the  fire.     The  lazy  bar  is  a  heavy  bar  of  iron,  bent  at  one  end  to 
hook  over  the  door  hinge  on  one  side,  while  the  other  end  rests 
on  the  catch.     The  part  extending  across  the  doorway  is  horizon- 
tal and  is  used  as  a  support  for  the  hoe  or  rake  while  the  fire  is 
being  cleaned  or  banked. 

9.  Classes  of  Boilers. — For  the  purpose  of  this  course,  boilers 


TYPES  OF  BOILERS  3 

will  be  divided  into  three  general  classes,  viz. :  Flue  boilers,  Fire- 
tube  boilers,  and  Water-tube  boilers.  These  three  classes  will 
include  most  of  the  boilers  in  use  to-day  but,  owing  to  the  great 
number  of  forms  being  sold,  some  will  necessarily  not  belong 
entirely  to  any  class  but  will  be  a  combination  of  two  or  more 
classes.  These  general  classes  may  be  further  subdivided,  as 
will  be  noted  later. 

The  simplest  type  of  boiler  that  can  be  imagined  is  the  plain 
cylinder  boiler  with  the  fire  beneath  it.  A  longitudinal  cross- 
section  of  such  a  boiler  is  shown  in  Fig.  1.  Although  such  boilers 
have  been  used  in  the  past,  they  are  seldom  seen  at  present 
as  they  are  very  wasteful  of  fuel.  They  have  the  advantage, 


FIG.  1. — Plain  cylindrical  boiler. 

however,  of  being  extremely  simple  and,  as  they  contain  a  large 
amount  of  water  compared  to  the  volume  of  the  steam  space, 
they  will  maintain  a  very  steady  pressure.  These  boilers, 
therefore,  do  not  require  close  attention.  For  these  reasons 
they  have  been  used  to  a  considerable  extent  in  small  power 
plants  for  buildings,  particularly  for  heating  purposes.  The 
plain  cylindrical  boiler  represents  the  first  step  in  the  develop- 
ment of  modern  power  boilers. 

The  next  step  in  the  development  of  the  boiler  was  the  put- 
ting of  a  flue  through  the  shell.     After  the  gases  from  the  fire  had 


4  STEAM  BOILERS 

passed  the  length  of  the  shell  they  were  directed  back  through 
this  flue,  and  more  heat  extracted.  With  the  use  of  this  flue 
began  the  practice  of  making  boilers  internally  fired.  The 
flues  were  made  large  enough  to  contain  the  grates.  In  this 
way  the  furnace  was  surrounded  by  water  on  all  sides  except 
in  front  and  at  the  rear.  After  the  gases  had  passed  through 
this  flue  they  were  lead  along  the  outside  of  the  shell  so  that 
more  heat  might  be  obtained  from  them. 

Following  certain  slight  modifications  of  this  type,  the  next 
development  was  the  fire-tube  boiler,  in  which  the  large  flue  was 
replaced  by  a  number  of  small  tubes.  This  greatly  increased  the 
heating  surface  and  made  a  much  more  efficient  boiler.  This 
type  is  still  the  most  common  in  the  United  States  for  station- 
ary steam  plants.  The  modern  locomotive  boiler  and  the 
Scotch  marine  boiler  are  modifications  of  this  type  for  locomotive 
and  marine  uses.  The  latest  development  is  the  water-tube 
boiler,  which  contains  the  water  within  a  number  of  small  tubes, 
thus  securing  the  maximum  heating  effect  combined  with  rapid- 
ity of  action. 

Flue  Boilers  are  those  having  one  or  more  large  flues  passing 
through  them.  The  grates  are  usually  placed  in  the  flues.  The 
name  "flue  boilers"  is  also  applied  to  boilers  having  the  fire 
outside  the  shell  and  having  flues  over  6  in.  in  diameter  passing 
through  the  shell. 

Fire-tube  Boilers  have  tubes  6  in.  or  less  in  diameter  passing 
lengthwise  through  the  shell.  The  hot  gases  pass  through  the 
tubes,  while  the  water  surrounds  them  on  the  outside.  Although 
the  name  "flues"  is  quite  commonly  applied  to  the  tubes  of 
fire-tube  boilers,  it  should  be  noted  that,  strickly  speaking,  the 
name  "flues"  applies  only  when  they  are  over  6  in.  in  diameter 
and  that  when  6  in.  or  less  they  are  "tubes." 

In  Water-tube  Boilers  the  water  is  contained  within  the  tubes 
while  the  hot  gases  pass  on  the  outside.  In  these  boilers  there 
are  no  very  large  drums  containing  great  volumes  of  water  and 
there  is  less  danger  from  explosion,  and  high  pressures  can  be 
carried  without  requiring  excessively  thick  sheets  of  steel. 

10.  Cornish  Boilers. — As  before  mentioned,  the  first  improve- 
ment on  the  plain  cylinder  boiler  was  the  addition  of  a  flue 
running  from  end  to  end.  The  flue  ran  entirely  through  the 
boiler  from  one  end  to  the  other  and  contained  the  grates  and 
bridge  wall.  This  arrangement  made  what  is  called  an  inter- 


TYPES  OF  BOILERS 


nally  fired  boiler,  that  is,  the  furnace  was  placed  inside  the  shell 
of  the  boiler  and  was  surrounded  by  water.  Boilers  of  this  form 
were  called  Cornish  boilers.  The 
heating  surface  formed  by  the  sides 
and  top  of  the  furnace  absorbed  a 
large  quantity  of  heat  and  was, 
therefore,  very  effective.  The 
heating  surface  was  further  ex- 
tended by  arranging  the  setting  of 
the  boiler  in  such  way  that  there 
were  two  passages  for  the  hot  gases, 
one  on  each  side  of  the  shell  and 
another  along  the  bottom.  The 
hot  gases  passed  first  through  the 
flue  inside  the  shell  to  the  back  of 
the  boiler;  at  this  point  they 
divided,  part  passing  to  the  front 
through  the  passage  on  one  side  of 
the  shell  and  the  other  part  passing 
along  the  other  side  of  the  shell. 
The  gases  then  reunited  and  passed 
to  the  back  through  the  passage 
along  the  bottom  of  the  shell  and 
out  the  stack.  Fig.  2  illustrates 
this  type  of  boiler.  This  view 
shows  clearly  the  internal  arrange- 
ment of  the  boiler,  including  the 
flue  passing  through  the  shell  and 
containing  the  grate  and  bridge 
wall.  The  view  shown  in  Fig.  3 
is  a  cross-section  of  the  same  boiler 
and  shows  the  arrangement  of  flues 
in  the  setting  for  leading  the  flue 
gases  along  the  sides  of  the  shell. 
The  name  "  Cornish  "  as  applied  to 
this  form  of  boiler  comes  from  the 
fact  that  it  was  first  used  at  the 
Cornish  mines  in  England.  Only 
those  boilers  which  have  a  single 
flue  are  known  as  Cornish  boilers.  This  boiler  was  a  great  im- 
provement over  the  cylindrical  boiler,  as  the  hot  furnace  gases 


6  STEAM  BOILERS 

were  made  to  pass  the  length  of  the  boiler  four  times,  and  thus 
a  larger  part  of  the  heat  might  be  extracted  from  the  gases. 
Cornish  boilers  were  made  in  sizes  up  to  28  ft.  long  by  7  ft.  in 
diameter  with  a  3-ft.  flue.  They  are  not  being  manufactured 
to  any  extent  at  present,  though  there  are  still  some  of  them 
in  use  in  some  of  the  older  power  plants  of  England. 

These  boilers  are  slow  steaming  on  account  of  the  large  mass  of 
water  in  them,  but  they  have  a  large  steam  space  and,  therefore, 
are  not  liable  to  sudden  fluctuations  in  pressure  with  changes  of 
load.  They  are  not  well  suited  to  high  pressures  owing  to  the 
difficulty  of  properly  bracing  the  heads  and  to  the  difficulty  in 
making  the  flue  strong  enough  to  withstand  the  crushing  pressures. 
In  Fig.  2  the  flue  is  shown  made  in  sections  with  the  ends  flanged 
outward  and  riveted  together.  This  construction  braces  it  and 
makes  it  much  stifTer  than  a  simple  straight '  flue  would  be. 
Another  method  of  stiffening  these  flues  is  to  make  them  of 
corrugated  sheets,  arranging  the  sheets  in  such  manner  as  to 
have  the  corrugations  pass  around  the  flue.  It  should  be  noted 
that  in  Fig.  2  the  flue  of  the  Cornish  boiler  is  supplied  with  Gallo- 
way tubes,  or  short  tubes  extending  across  the  flue.  The 
Cornish  boiler  may  or  may  not  have  these  Galloway  tubes,  as 
will  be  noted  later. 

11.  Lancashire  Boilers. — The  next  form  of  boiler  to  be  devel- 
oped was  what  is  known  as  the  Lancashire  boiler.  This  is  also 
an  English  type  very  similar  in  construction  to  the  Cornish  boiler 
but  differing  from  it  in  having  two  flues  instead  of  one.  These 
two  flues  may  extend  through  the  boiler  separately  but  in  some 
cases  they  are  joined  together  just  back  of  the  bridge  wall, 
forming  a  single  flue  which  extends  from  this  point  to  the  rear 
end  of  the  boiler,  and  also  forming  a  common  combustion 
chamber  for  gases  from  the  two  grates.  In  England,  this  type 
is  given  the  name  of  "  breeches  "  boiler.  The  two  furnaces  may 
be  fired  alternately  and  the  gases  from  the  freshly  fired  grate 
will  be  burned  in  the  combustion  chamber  by  the  air  that  passes 
through  the  other  grate.  In  this  way  a  uniformly  high  tempera- 
ture is  maintained  in  the  combustion  chamber. 

The  Lancashire  is  usually  somewhat  larger  than  the  Cornish 
boiler  and  has  more  heating  surface  for  the  same  outside  dimen- 
sions. As  this  additional  heating  surface  forms  the  walls  of  the 
fire  box,  it  is  very  effective.  Just  as  with  the  Cornish  boiler, 


TYPES  OF  BOILERS  7 

the  Lancashire  may  or  may  not  have  Galloway  tubes.  The 
setting  for  the  Lancashire  boiler  is  the  same  as  for  the  Co.rnish. 
These  boilers  are  usually  from  7  to  8  ft.  in  diameter  and  about 
30  ft.  long,  with  flues  30  in.  to  40  in.  in  diameter. 

12.  Galloway  Boilers. — -Any  boiler  whose  flue  is  supplied  with 
Galloway  tubes,  whether  it  be  of  the  Cornish  or  Lancashire  type, 
is  known  as  a  Galloway  Boiler.     Galloway  tubes  are  tapered 
tubes  extending  through  the  flue  from  bottom  to  top  as  shown 
in  Fig.  2.     These  tubes  stiffen  the  flues;  they  add  very  effective 
heating  surface,  since  they  are  directly  in  the  path  of  the  hot- 
test gases;  and  they  maintain  a  good  circulation  of  the  water  in 
the  boiler.  .  The  tapered  form  makes  the  tubes  easy  to  put  in  and 
to  replace,  since  the  flange  on  the  smaller  end  passes  through  the 
hole  for  the  larger  end.     The  end  flanges  are  riveted  to  the  flue. 

The  settings  for  Lancashire  and  Galloway  boilers  are  similar  to 
that  shown  for  the  Cornish  boiler,  though  the  Galloway  boilers 
sometimes  have  but  one  pass  for  the  gases  along  the  outside  of 
the  shell.  This  is  permissible  because  the  Galloway  tubes  ex- 
tract considerable  heat  from  the  gases  before  they  reach  the 
rear  of  the  boiler. 

All  of  the  boilers  so  far  described  are  internally  fired  except 
the  plain  cylindrical  boiler.  Boilers  of  these  types  are  seldom 
used  for  pressures  greater  than  100  Ib.  per  square  inch.  They 
are  rarely  seen  in  the  United  States,  though  they  are  quite  common 
abroad,  especially  in  England.  They  are  slow  steamers  but  will 
maintain  a  steady  pressure  on  account  of  the  large  volume  of 
water  which  they  contain. 

13.  Fire-tube  Boilers. — Fire-tube  boilers  are  more  commonly 
used  than  any  other  kind.     They  are  simple  in  construction, 
comparatively  cheap,  and  are  quite  durable  when  they  receive 
proper  care.     The  heating  surface  is  large  for  the  space  it  occupies 
and,  therefore,  the  boiler  will  occupy  but  small  space  in  proportion 
to  its  steaming  capacity.     It  is  a  fairly  rapid  steamer,  with  large 
steam  space,  and  is  well  suited  to  pressures  up  to  150  Ib.     This 
boiler  came  into  use  before  the  water-tube  type  and  this,  together 
with  its  simplicity  and  ease  of  attendance,  accounts  for  the  large 
number  in  use. 

Fire-tube  boilers  are  made  in  a  variety  of  forms.  They  may 
be  either  externally  or  internally  fired,  and  either  horizontal  or 
vertical.  Large  sizes  are  practically  all  horizontal,  except  the 


STEAM  BOILERS 


FIG.  4. — Horizontal  fire-tube  boiler  with  dome. 


FIG.  5. — Horizontal  fire-tube  boiler  with  flush  front  setting. 


TYPES  OF  BOILERS  9 

Manning  boiler,  mentioned  later;  while  the  very  small  sizes  are 
practically  all  vertical. 

The  most  common  form  of  fire-tube  boiler  for  stationary 
purposes  is  the  externally  fired  horizontal  fire-tube  boiler  shown 
in  Fig.  4.  This  boiler,  without  the  dome,  is  also  shown  with  its 
setting  in  Fig.  5.  The  shell  is  cylindrical  in  form  with  flat  heads, 
and  the  tubes,  which  are  from  2  to  4  in.  in  diameter,  pass  through 
the  shell  from  one  head  to  the  other. 

In  the  form  of  boiler  shown  in  Figs.  4  and  5  the  smoke  connection 
is  made  a  part  of  the  shell,  being  riveted  to  the  front  end.  The 
hot  gases  pass  along  the  bottom  of  the  shell  from  front  to  back  and 
then  to  the  front  again  through  the  tubes.  Since  there  are  a 
large  number  of  tubes  of  small  diameter,  the  surface  of  these 
tubes  forms  the  principal  part  of  the  heating  surface. 

Sometimes  this  form  of  boiler  is  set  so  the  hot  gases  pass  along 
the  bottom  of  the  shell  from  front  to  back  and  then  to  the  front 
through  the  tubes,  and  the  setting  is  so  arranged  that  the  gases 
may  then  pass  to  the  back  again  in  the  space  between  the  top 
of  the  shell  and  the  setting,  giving  the  heat  in  the  gases  a  further 
chance  to  be  absorbed  by  the  boiler.  The  extra  heating  surface 
added  in  this  way  is  not  very  effective  since  the  larger  part  of 
it  has  steam  on  one  side  of  the  metal  and  hot  gases  on  the  other. 
Heat  transmission  through  the  metal  under  such  conditions  is 
not  so  rapid  as  if  there  were  water  on  one  side  of  the  metal. 

The  water  line  in  this  boiler  is  carried  about  3  in.  above  the 
top  row  of  tubes  and  all  the  space  in  the  shell  above  this  is  the 
steam  space.  In  addition  to  this  steam  space,  a  steam  dome 
is  sometimes  placed  on  top  of  the  shell,  increasing  the  volume  of 
the  steam  space  and  also  allowing  the  steam  to  be  taken  from 
the  boiler  at  a  point  somewhat  removed  from  the  surface  of  the 
water.  This  insures  a  supply  of  steam  drier  than  if  the  supply 
was  taken  directly  from  the  shell. 

Fig.  5  shows  a  boiler  supported  by  means  of  two  brackets  on 
each  side,  one  near  the  front  and  the  other  near  the  back.  The 
front  ones  rest  directly  on  the  side  walls,  thus  holding  the  front 
end  of  the  boiler  stationary,  while  the  back  ones  rest  on  iron 
rollers  placed  on  cast-iron  plates  which  rest  on  the  side  walls. 
This  allows  the  back  end  of  the  boiler  to  move  as  the  shell  expands, 
without  injuring  the  side  walls  or  front  setting.  The  setting 
for  this  type  of  boiler  is  described  in  detail  in  a  later  chapter. 


STEAM  BOILERS 


FIG.  6. — Portable  fire-tube  boiler  on  skids. 


FIG.  7. — Longitudinal  section  of  portable  fire-tube  boiler. 


TYPES  OF  BOILERS  11 

14.  Portable  Boilers. — A  portable  boiler  is  one  which  requires 
no  built-up  setting  and  which  can  therefore  be  easily  moved 
from  place  to  place.     This  type  of  boiler  is  often  used  in  small 
saw  mills  and  other  small  and  isolated  power  plants,  and  where 
it  may  be  desirable  to  change  the  location  of  the  boiler  after  a 
time.     Portable  boilers  are  practically  always  of  the   fire-tube 
type. 

An  example  of  a  small  fire-tube  portable  boiler  is  shown  in 
Fig.  6.  In  this  boiler  the  fire  box  is  made  of  cast-iron  plates 
riveted  to  and  beneath  the  front  end  of  the  boiler  shell.  The 
fire  box  is  lined  with  brick  to  prevent  the  heat  from  destroying 
the  cast-iron  plates.  The  boiler  and  furnace  are  mounted  on 
skids  so  it  may  be  easily 'moved. 

Fig.  7  is  a  longitudinal  section  of  the  same  boiler  and  shows 
the  location  of  the  fire  tubes  and  the  path  of  the  hot  gases.  The 
tubes  are  in  two  sets;  one  of  short  tubes  which  connect  the  fire 
box  with  the  combustion  chamber  at  the  back  of  the  shell;  and 
the  other  of  longer  tubes  which  connect  the  combustion  chamber 
with  the  smoke  chamber  at  the  front  of  the  shell.  The  path  of 
the  hot  gases  is  from  the  fire  box  through  the  short  tubes  to 
the  combustion  chamber  and  from  the  combustion  chamber 
through  the  long  tubes  to  the  smoke  chamber.  As  a  short  and 
light  steel  stack  is  used  on  these  boilers,  its  weight  is  carried 
directly  on  the  front  end  of  the  shell.  Fig.  7  also  illustrates  the 
method  of  staying  that  part  of  the  heads  which  lies  above  the 
tubes. 

15.  Locomotive  Boilers. — The  locomotive  boiler  is  named  from 
its  shape,  that  of  the  boiler  used  on  locomotives.     It  is  a  fire- 
tube  boiler  and  is  internally  fired,  that  is,  the  furnace  is  sur- 
rounded by  water.     This  is  made  possible  by  extending  the  shell 
downward  to  form  the  sides  of  the  furnace  or  fire  box.     The 
walls  of  the  furnace  are  made  double  with  a  space  between  the 
side  plates  which  is  connected  directly  with  the  water  space  in 
the  shell  and  thus  forms  a  water  leg. 

Fig.  8  shows  a  small  portable  locomotive  boiler  mounted  on 
skids.  These  boilers  are  made  only  in  small  sizes  and  are  often 
used  in  isolated  locations  where  only  a  small  amount  of  power  is 
used.  The  barrel  or  shell  of  the  boiler  is  cylindrical  in  shape  and 
contains  a  large  number  of  small  tubes.  The  hot  gases  leaving 
the  furnace  pass  through  these  small  tubes,  which  are  surrounded 
by  water,  to  the  smoke  chamber  at  the  back  of  the  shell,  thus 


12  STEAM  BOILERS 

passing  the  length  of  the  boiler  but  once.  The  small  steel  smoke 
stack  rests  directly  on  the  shell. 

These  boilers  are  usually  provided  with  a  steam  dome  from 
the  top  of  which  the  supply  of  steam  is  taken,  thus  securing  a 
drier  supply  than  if  taken  from  a  point  nearer  the  water  line. 

A  locomotive  boiler  such  as  is  used  on  locomotives  is  shown 
in  Figs.  9  and  10.  The  shell  of  the  locomotive  boiler  is  cylindrical 
and  the  furnace  is  attached  to  the  front  of  the  boiler  as  shown 
in  Fig.  10.  A  large  number  of  small  tubes  pass  through  the 
cylindrical  part  of  the  shell,  giving  a  large  amount  of  heating 
surface.  The  sides  of  the  furnace  form  a  continuation  of  the 


FIG.  8. — Portable  locomotive  boiler  on  skids. 


shell  and  are  formed  into  water  legs  extending  down  the  sides, 
front,  and  back  of  the  furnace.  The  water  legs  are  thoroughly 
braced  by  means  of  short  bolts  which  extend  through  the  water 
legs  and  which  have  nuts  on  both  ends,  or  are  riveted  over.  In 
the  form  shown  in  Fig.  9,  which  is  known  as  the  " wagon-top" 
boiler,  there  is  considerable  pressure  exerted  on  the  crown  sheet 
which  is  the  sheet  directly  over  the  furnace.  This  accounts  for 
the  large  numbers  of  stays  which  extend  from  the  crown  sheet 
to  the  top  of  the  shell.  As  these  stays  .are  not  perpendicular  to 
the  surface  of  either  the  crown  sheet  or  the  shell,  the  calculation 


TYPES  OF  BOILERS 


13 


14 


STEAM  BOILERS 


of  their  strength  is  rather  uncertain.  To  simplify  this,  the 
furnace  is  sometimes  made  in  the  shape  shown  in  Fig.  11,  having 
all  opposing  sides  parallel  to  each  other  and  the  stays  perpen- 
dicular to  the  surfaces  which  they  support. 


FIG.  11. — Belpaire  locomotive  fire  box. 

16.  Scotch  Marine  Boilers. — The  Scotch  marine  type  of  holier 
is  shown  in  Figs.  12,  13,  and  14.  It  is  very  large  in  diameter 
and  comparatively  short  in  length,  which  is  a  shape  best  suited 
to  fitting  into  the  hulls  of  steamships,  where  it  is  most  commonly 
used'.  In  this  boiler  the  grates  are  placed  in  flues  as  shown, 
there  being  one,  two,  three,  or  even  four  of  these  flues,  depending 
on  the  size  of  the  boiler.  Just  back  of  the  bridge  wall,  which 
is  also  in  the  flue,  the  flue  is  enlarged  into  a  combustion  chamber. 
After  leaving  the  combustion  chamber  the  hot  gases  pass  to  the 
front  of  the  boiler  through  a  large  number  of  fire  tubes  and 
then  out  of  the  stack,  which  is  connected  to  the  front  of  the  boiler. 
Sometimes  two  of  these  boilers  are  placed  back  to  back  with  a 
common  combustion  chamber  and  with  the  smoke  stacks  from 
each  uniting  into  one  above  the  boilers.  As  the  heads  of  the 
boilers  are  flat  and  very  large  they  require  strong  bracing. 
Therefore,  a  number  of  rods  are  run  entirely  through  the  boiler 
from  the  front  to  the  back  head,  being  held  by  nuts  on  each  end. 


TYPES  OF  BOILERS  15 

In  addition  to  this  bracing,  some  of  the  tubes  are  made  extra 
heavy  and  are  threaded  and  screwed  into  the  heads  so  they 
may  act  as  braces.  This  boiler  requires  no  setting  and  is 
supported  on  large  cast-iron  yokes  which  are  bolted  to  the 
bottom  of  the  ship  or  to  the  floor.  The  Scotch  marine  boiler 
is  used  very  extensively  in  steamships  and  has  given  excellent 
service. 

The  Scotch  marine  boiler  described  above  is  known  as  a  "  wet- 
back" boiler  and  is  used  principally  on  vessels.     This  type  of 


FIG.  12.- — Scotch  marine  boiler. 

boiler  is  modified  somewhat  for  stationary  work,  being  longer 
in  proportion  to  its  diameter  and  having  a  "dry  back."  A 
"  dry  -back"  boiler  of  the  Scotch  marine  type  is  illustrated  in 
Fig.  15,  from  which  it  will  be  seen  that  the  back  of  the  boiler 
is  protected  by  a  brickwork  lining  instead  of  a  water  leg.  The 
grates  and  bridge  wall  are  placed  inside  a  corrugated  flue,  the 
corrugations  being  for  the  purpose  of  giving  additional  strength 
to  the  flue  and  for  making  it  flexible  enough  to  take  up  expansion. 
The  hot  gases  pass  from  the  furnace  to  the  combustion  chamber 
at  the  back  of  the  boiler  and  thence  forward  through  the  tubes 
to  the  smoke  connection  at  the  front.  The  space  inside  the 


16 


STEAM  BOILERS 


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TYPES  OF  BOILERS  17 

shell,  above  and  at  the  sides  of  the  flue,  is  filled  with  fire  tubes, 
giving  a  large  amount  of  heating  surface.  The  flat  surfaces  of 
the  heads  which  are  not  occupied  by  the  flue  or  tubes  are  braced 
by  rods  extending  through  the  shell  from  one  head  to  the  other. 


FIG.   15. — Dry  back  Scotch  marine  boiler. 

17.  Vertical  Fire -tube  Boilers. — The  vertical  fire-tube  boiler 
is  often  used  in  places  where  there  is  not  much  floor  space  and 
also  where  a  light,  easily  portable  boiler  is  required,  such  as  for 
supplying  steam  to  hoisting  engines.  Vertical  fire-tube  boilers 
are  usually  internally  fired,  the  furnace  being  completely  sur- 
rounded with  water,  except  the  bottom,  which  is  used  as  an  ash 
pit.  The  tubes  lead  directly  from  the  top  of  the  furnace  to  the 
smoke  connection  at  the  top,  thus  allowing  the  hot  gases  to  pass 
the  length  of  the  boiler  but  once. 

In  the  form  of  a  small  vertical  fire-tube  boiler  shown  in  Fig.  16 
the  tops  of  the  tubes  are  above  the  water  level  and  are  thus 
exposed  to  the  high  temperature  of  the  flue  gases  on  one  side 
and  to  steam  on  the  other.  Thus  they  are  liable  to  become 
overheated  and  to  leak  from  unequal  expansion  between  them 
and  the  head  when  the  boiler  is  forced.  To  prevent  injury  from 
this  cause,  these  boilers  are  sometimes  made  in  the  form  shown 
in  Fig.  17,  in  which  the  ends  of  the  tubes  are  below  the  water 


18 


STEAM  BOILERS 


level  or  are  submerged.  The  submerged  type  has  the  disad- 
vantage, however,  of  not  having  a  large  or  free  disengagement 
surface,  and  steam  is  apt  to  collect  under  the  top  sheet  and 
blow  water  into  the  steam  connection. 

A  type  of  large  vertical  fire-tube  boiler,  known  as  the  Man- 
ning boiler,  is  shown  in  Fig.  18.     The  tubes  of  this  boiler  are 


FIG.  16. — Small  vertical  boiler.       FIG.   17. — Vertical  boiler  with  sub- 
merged tube  sheet. 


usually  about  2  1/2  in.  in  diameter  and  from  12  to  15  ft.  long, 
extending  from  the  crown  sheet  just  over  the  furnace  to  the 
smoke  connection  on  top.  The  part  of  the  boiler  forming  the 
furnace  is  made  larger  than  the  shell  in  order  to  allow  more 
grate  area  and,  by  forming  a  horizontal  ring  around  the  boiler, 
to  permit  expansion  and  contraction  between  the  furnace  and 
the  shell  without  straining  the  joints. 


TYPES  OF  BOILERS 


19 


FIG.  18. — Manning  vertical  boiler. 


CHAPTER  II 
WATER-TUBE  BOILERS 

18.  Water -tube  Boilers. — As  stated  in  the  previous  chapter, 
water-tube  boilers  are  those  which  carry  the  water  on  the  inside 
of  the  tubes,  while  the  hot  gases  are  circulated  on  the  outside. 
Water-tube   boilers  are  made  in  a  great  variety  of  forms,  dif- 
fering from  each  other  in  details  of  construction,  but  being 
alike  in  principle.     The  more  important  forms  of   water-tube 
boilers  are  illustrated  in  this  chapter. 

The  water-tube  boiler,  which  represents  the  latest  type  of 
boiler  construction,  has  been  brought  into  extensive  use  by  the 
demand  for  a  boiler  to  withstand  high  pressures.  In  this  type 
of  boiler,  the  water  is  divided  into  elements  of  small  size.  This 
permits  the  walls  of  the  parts  containing  the  water  to  be  much 
thicker  in  proportion  to  the  area  exposed  to  pressure,  thus 
giving  the  boiler  great  strength.  Dividing  the  water  into  small 
elements  also  has  the  advantage  of  exposing  a  large  surface  for 
the  absorption  of  heat.  This  makes  a  rapid  steaming  boiler 
and  one  which  can  be  forced  readily,  but  it  also  requires  that 
the  boiler  be  closely  watched  as  it  contains  only  a  small  amount 
of  water,  which  may  go  below  the  low-water  level  quickly. 

19.  Babcock  and  Wilcox  Boilers. — Fig.   19  shows  a  type  of 
water-tube    boiler   known  as  the   Babcock  and  Wilcox.     This 
was  the  first  type  of   water-tube  boiler  placed  on  the  market 
and,  as  it  was  patented,  it  was  on  the  market  for  some  time 
before  other  types  were  introduced.     Hence,  there  are  more  of 
them  in  use  than  of  others. 

The  B.  &  W.  boiler  consists  of  a  number  of  straight  tubes 
connected  into  steel  or  cast-iron  headers  at  the  ends,  the  headers 
being  connected  to  the  horizontal  steam  drum  at  the  top.  The 
end  connections  are  made  in  sections;  each  holding  two  vertical 
rows  of  tubes.  A  number  of  headers  are  placed  side  by  side 
to  make  up  the  complete  set  of  tubes.  The  headers  are  in  the 

21 


22 


STEAM  BOILERS 


form  of  hollow  steel  boxes.  Holes  are  bored  in  the  back  of 
the  header  into  which  the  ends  of  the  tubes  are  expanded, 
and  other  holes,  called  handholes,  are  bored  in  the  front  side  of 
the  header  directly  opposite  the  ends  of  the  tubes,  in  order 
that  a  cleaner  may  be  introduced  through  them  into  the  tubes 
and  scale  or  other  deposits  cleaned  from  the  inside.  The  hand- 
holes  are  closed  by  means  of  handhole  covers  which  are  made 
steam-  and  water-tight  by  means  of  gaskets. 

The  steam  drums  vary  in  size  from  18  to  42  in.  in  diameter 
and  are  from  16  to  20  ft.  long.     A  mud  drum,  for  collecting  mud 


FIG.   19. — Babcock  and  Wilcox  water-tube  boiler. 


and  sediment  which  may  be  brought  in  by  the  feed  water,  is 
placed  at  the  back  end  of  the  tubes  at  their  lowest  point.  This 
is  a  good  location  for  the  mud  drum  as  the  feed  water  will  be 
heated  sufficiently  by  the  time  it  reaches  the  drum  to  deposit  the 
greater  part  of  its  scale-forming  impurities.  The  water  flows 
downward  in  the  back  headers  and  the  impurities,  being  heavier, 
continue  downward  and  settle  in  the  mud  drum. 

The  feed  pipe  enters  through  the  front  head  of  the  steam  drum 
as  shown  in  Fig.  20.  The  direction  of  circulation  of  the  water 
in  the  boiler  is  through  the  tubes  from  the  back  to  the  front  and 


WATER-TUBE  BOILERS 


23 


then  up  through  the  front  headers  into  the  steam  drum,  carrying 
the  steam  bubbles  along  with  it.  The  water  passes  to  the  back 
through  the  steam  drum  and  down  the  back  headers  to  the 
tubes.  The  tubes  slope  upward  toward  the  front  and  this  aids 
the  circulation,  as  hot  water  always  tends  to  rise.  Fig.  20  shows 
clearly  the  construction  of  the  front  end  of  the  steam  drum  and 
the  connection  of  the  headers  at  the  front  of  the  boiler.  A 
deflector  plate  is  placed  in  the  steam  drum  immediately  in  front 
of  the  front  header  connections.  This  is  for  the  purpose  of 


FIG.  20. — Partial  section  of  B.  and  W.  water-tube  boiler. 


deflecting  the  current  of  water  rising  through  the  front  headers 
toward  the  back  of  the  steam  drum,  thus  helping  to  give  a  more 
positive  circulation.  Fig.  19  shows  this  boiler  with  inclined 
headers,  while  Fig.  20  shows  it  with  vertical  headers,  which  per- 
mit of  a  shorter  setting. 

The  construction  and  location  of  the  handholes  and  covers 
is  also  shown  by  Fig.  20.  The  removal  of  a  handhole  cover 
permits  ready  access  to  the  tube  immediately  back  of  it  and,  as 


24  STEAM  BOILERS 

the  tubes  are  straight,  the  inside  may  be  examined  if  a  lighted 
candle  or  lamp  is  held  in  front  of  one  end  of  the  tube  while  the 
eye  is  held  at  the  other  end. 

The  hot  gases  leaving  the  grate  are  made  to  pass  across  the 
tubes  by  means  of  the  baffle  plates  placed  across  them;  then 
they  pass  downward  across  the  tubes  again  into  the  combustion 
chamber  back  of  the  bridge  wall;  and  then  upward  again  across 
the  tubes  and  out  at  the  smoke  connection  which  leads  out  from 
the  back  of  the  boiler. 

This  form  of  boiler  is  not  supported  from  the  side  walls  as  is 
done  in  the  case  of  some  fire-tube  boilers,  but  it  is  suspended  by 
means  of  straps  passing  under  the  steam  drum  and  connected  to 
I-beams  across  the  top  of  the  boiler.  These  beams  are  sup- 
ported by  steel  columns  built  into  the  side  walls.  The  boiler  is 
thus  independent  of  the  setting  and  is  free  to  expand  and  con- 
tract without  injuring  the  brickwork.  Long,  narrow  doors  are 
provided  in  the  side  walls,  through  which  a  steam-hose  may  be 
inserted  for  blowing  soot  and  ashes  off  the  tubes. 

20.  Murray  Water-tube  Boiler. — A  type  of  water-tube  boiler 
which  is  manufactured  by  a  number  of  firms  is  shown  in  Fig  21. 
The  one  illustrated  here  is  a  Murray  water-tube  boiler.  It  has 
the  large  drum  on  top  placed  parallel  with  the  tubes,  and  the 
end  connections  made  into  one  large  box  instead  of  being  divided 
into  sections  as  in  the  B.  &  W.  This  boiler  is  set  very  much  the 
same  as  the  B.  &  W.  boiler.  The  back  ends  of  the  tubes  are 
placed  lower  than  the  front  ends  and,  as  the  drum  is  parallel 
with  the  tubes,  this  throws  the  drum  into  an  inclined  position. 
As  the  water  line  must  come  above  the  ends  of  all  the  tubes,  this 
causes  the  back  end  of  the  drum  to  be  almost  completely  filled 
with  water  and  allows  very  little  steam  space  at  this  end.  In 
order  to  secure  dry  steam,  the  steam  connection  is  taken  from 
the  front  part  of  the  drum,  where  the  end  of  the  pipe  may  be  as  far 
removed  from  the  surface  of  the  water  as  possible  and,  as  an  addi- 
tional safeguard  in  preventing  water  from  entering  the  steam  pipe, 
a  dry  pipe  is  connected  to  it.  In  some  cases,  this  type  of  boiler 
has  an  extra  drum  placed  above  and  across  the  front  end  of  the 
main  drum,  the  two  being  connected  by  a  very  short  length  of 
flanged  pipe.  This  gives  more  steam  space  and  acts  as  an  addi- 
tional safeguard  in  securing  dry  steam,  as  the  steam  pipe  is  taken 
from  the  top  of  the  auxiliary  drum. 


WATER-TUBE  BOILERS 


25 


The  drum  of  this  boiler  is  also  provided  with  a  baffle  plate 
near  the  front  and  above  the  connection  of  the  front  header. 
The  baffle  plate  serves  the  double  purpose  of  directing  the 
circulation  and,  since  the  steam  connection  is  made  in  front  of 
the  baffle  plate,  it  aids  in  preventing  water  from  entering  the 
steam  pipe. 

The  hot  gases  travel  parallel  to  the  tubes  instead  of  across 
them,  as  in  the  B.  &  W.  boiler.  They  are  made  to  take  this 


FIG.  21. — Murray  water-tube  boiler. 


direction  by  the  layers  of  tile  which  are  placed  on  certain  tubes 
as  shown  in  the  illustration.  The  path  of  the  gases  is  from  the 
grate  over  the  bridge  wall  to  the  rear  of  the  boiler;  they  then 
return  to  the  front  along  the  tubes  and  between  the  two  layers 
of  tile;  then  they  rise  to  the  steam  drum  and  follow  along  it  to 
the  smoke  uptake  which  is  placed  at  the  rear  of  the  boiler. 

21.  Edge  Moor  Water -tube  Boiler. — The  Edge  Moor  water- 
tube  boiler  shown  in  Fig.  22  is  somewhat  similar  to  the  Murray 
boiler,  just  described,  in  that  each  end  connection  is  a  single  box 
made  from  riveted  sheets  of  steel.  The  steam  drums,  however, 
are  placed  horizontally,  while  the  tubes  are  inclined  as  in  the 


26  STEAM  BOILERS 

types  just  described.  There  may  be  one  or  more  drums, 
depending  on  the  size  of  the  boiler. 

In  the  Edge  Moor  boiler  the  end  connections  are  placed  at  the 
ends  of  the  drums  and  the  drums  are  riveted  directly  to  the  back 
sheets  of  the  headers,  thus  giving  a  very  simple  construction. 
An  opening  as  large  as  the  drums  is  made  in  the  outside  sheets 
of  the  headers,  and  these  openings  are  covered  by  dished  cover 
plates. 

The  tubes  are  expanded  into  the  back  sheets  of  the  headers 


FIG.  22. — Edge  Moor  water-tube  boiler. 


and  an  oval-shaped  handhole  is  directly  opposite  each  tube. 
The  handholes  are  flanged  inward  to  give  greater  strength,  and 
the  cover  plate  is  on  the  inside  of  the  header  where  the  steam 
pressure  keeps  it  tightly  to  its  seat.  The  opposing  sheets  of  the 
header  are  braced  by  stay  bolts  placed  between  the  handholes 
and  riveted  to  the  sheets. 

The  construction  of  the  headers  and  drums,  described  above, 
gives  a  large  and  free  area  for  the  passage  of  water  and  the  circula- 
tion is  not  likely  to  be  clogged  when  the  boiler  is  forced. 


WATER-TUBE  BOILERS 


27 


In  the  Edge  Moor  boiler  shown  here,  the  path  of  the  flue 
gases  is  the  same  as  that  described  in  connection  with  the  B.  &W. 
boiler,  but,  of  course,  the  gases  may,  by  a  rearrangement  of  the 
tile  baffle  plates,  be  made  to  follow  a  path  similar  to  that  described 
in  connection  with  the  Murray  boiler,  provided  the  tube  spacing 
will  give  the  requisite  area. 

22.  Atlas  Water -tube  Boiler. — The  Atlas  water-tube  boiler 
illustrated  in  Fig.  23  shows  a  radical  depature  in  design  from 
the  types  shown  before.  The  tubes  of  this  boiler  are  inclined, 
though  not  so  steeply  as  in  the  B.  &  W.,  and  the  path  of  the 


FIG.  23. — Atlas  water-tube  boiler. 


flue  gases  is  the  same  as  in  that  boiler.  The  headers  are  con- 
structed like  those  of  the  Murray  boiler. 

Instead  of  having  a  single  steam  drum  placed  lengthwise  of 
the  boiler,  the  Atlas  boiler  is  provided  with  three  drums  which 
are  placed  across  it.  The  advantage  in  this  arrangement  of 
the  drums  is  that  it  allows  a  cheaper  and,  at  the  same  time,  a 
stronger  connection  between  the  header  and  drums. 

The  front  and  rear  drums  are  larger  than  the  middle  one, 
which  is  used  entirely  as  a  steam  drum.  The  normal  water 
level  is  about  the  middle  of  the  two  lower  drums.  These  two 
drums  are  connected  below  the  water  line  by  a  series  of  tubes. 


28  STEAM  BOILERS 

The  circulation  is  in  the  same  direction  as  in  the  B.  &  W.  boiler. 
The  steam  drum  is  connected  to  both  the  front  and  rear  drums 
above  the  water  line  in  order  to  collect  steam  from  them,  although 
the  larger  part  of  the  steam  comes  from  the  front  drum.  The 
steam  connection  is  to  the  middle  dram  where  the  driest  steam 
may  be  obtained. 

The  feed  water  is  led  into  the  rear  drum,  where  it  is  discharged 
at  the  bottom  of  a  deep  trough.  Here  it  has  an  opportunity  to 
become  heated  and  deposit  most  of  its  scale-forming  impurities 
before  it  overflows  the  trough  and  enters  the  circulation  path. 

23.  Stirling  Water -tube  Boiler. — The  water-tube  boiler  shown  in 
Fig.  24  has  come  into  extensive  use  within  recent  years,  and  is 
proving  very  satisfactory.  This  is  the  Stirling  boiler  and,  as  may 
be  seen  from  Fig.  24,  it  differs  greatly  from  any  of  the  forms  of 
water-tube  boilers  previously  described.  The  boiler  consists 
of  three  horizontal  drums  at  the  top  and  one  at  the  bottom. 
Each  one  of  the  top  drums  is  connected  to  the  bottom  drum  by 
a  number  of  water  tubes,  some  of  which  are  bent  in  order  that 
they  may  enter  the  drums  at  right  angles  to  the  surface.  The 
bent  tubes  are  a  disadvantage  in  that  they  are  hard  to  examine. 
A  straight  tube  may  be  examined  by  looking  in  one  end  of  the 
tube  while  a  light  is  held  to  the  other  end,  but  this  cannot  be 
done  with  bent  tubes. 

The  path  of  the  flue  gases  is  from  the  furnace  over  the  bridge 
wall  and  along  the  front  set  of  tubes  to  the  front  drum  at  the 
top.  From  here  it  passes  over  to  the  second  set  of  tubes  and 
follows  these  down  to  the  bottom  drum  where  it  crosses  to  the 
rear  set  of  tubes  and  follows  these  to  the  top,  where  the  smoke 
connection  is  made.  From  this  it  is  seen  that  the  hot  gases  are 
in  contact  with  the  tubes  for  a  considerable  distance,  which 
allows  a  large  part  of  the  heat  in  them  to  be  extracted. 

The  two  front  drums  at  the  top  are  connected  by  two  sets 
of  cross  tubes,  one  set  connecting  the  tops  of  the  drums  and 
the  other  connecting  the  bottoms.  The  circulation  of  the 
water  is  as  follows:  The  water  is  fed  into  the  upper  rear  drum, 
passes  down  the  rear  bank  of  tubes  to  the  lower  drum,  thence 
up  the  front  bank  to  the  front  drum.  Here  the  steam  formed 
during  the  passage  up  the  front  bank  of  tubes  is  disengaged  and 
passes  through  the  upper  row  of  cross  tubes  to  the  middle  drum, 
while  the  water  passes  through  the  lower  row  of  cross  tubes  to 


WATER-TUBE  BOILERS 


29 


the  middle  drum,  thence  down  the  middle  bank  of  tubes  to  the 
lower  drum,  from  which  it  is  again  drawn  up  the  front  bank  to 
continue  this  course  until  it  is  evaporated.  Steam  is  taken 
from  the  top  of  the  middle  drum  and  the  steam  spaces  in  the 
other  two  top  drums  are  connected  to  the  steam  space  of  the 
middle  drum. 


FIG.  24. — Stirling  water-tube  boiler. 


The  bottom  drum  serves  as  a  mud  drum  for  collecting  mud  and 
sediment,  which  settles  as  the  water  is  heated.  The  blow-off 
is  connected  to  the  bottom  of  this  drum. 

The  shape  of  the  Stirling  boiler  is  such  that  it  occupies  only 
a  small  amount  of  floor  space  for  a  given  power  and  hence  it  is 
used  largely  where  land  is  valuable. 

24.  Vogt  Water -tube  Boiler.— The  Vogt  water-tube  boiler  is 


30 


STEAM  BOILERS 


another  rather  distinct  form.  The  steam  drum  is  horizontal, 
as  in  other  forms,  but  the  arrangement  of  the  tubes  is  quite 
different.  As  seen  in  Fig.  25  there  are  three  sets  of  slightly 
inclined  tubes  along  which  the  flue  gases  travel,  thus  passing 
the  length  of  the  boiler  three  times. 

The  circulation  is  upward  through  the  sets  of  inclined  tubes 
to  the  steam  drum,  where  the  steam  is  released.     The  water 


FIG.  25. — Vogt  water-tube  boiler. 


then  passes  along  the  steam  drum  to  the  rear,  whence  it  flows 
down  through  the  vertical  downcast  tubes  to  the  mud  drum  and 
from  there  into  the  inclined  tubes  again.  The  feed  water  enters 
the  steam  drum  on  top  near  the  rear  and  discharges  downward 
into  the  downcast  tubes. 

The  arrangement  of  tubes  used  in  this  boiler  gives  great  flex- 


WATER-TUBE  BOILERS  31 

ibility  against  expansion  and  contraction,  while  retaining  straight 
tubes,  but  in  order  to  accomplish  this  advantage  some  rather 
complicated  flanging  and  riveting  is  required. 

25.  Vertical  Water -tube  Boilers. — There  has  been  considerable 
demand  in  recent  years  for  a  boiler  of  large  power  which  would 
occupy  but  small  floor  space,  and  the  vertical  water-tube  boiler 
has  been  designed   to   meet   these   conditions.     Practically   all 
vertical  water-tube  boilers  consist  of  large  drums  at  the  top  and 
bottom  and  a  series  of  water  tubes  placed  vertically,  or  nearly 
so,    connecting    these    drums.     This    construction    places    the 
tubes  in  the  best  position  for  promoting  a  rapid  circulation,  as 
water  tends  to  rise  when  heated,  and  the  more  nearly  vertical 
the  tube,  the  faster  it  will  rise. 

26.  Wickes  Vertical  Water-tube   Boiler. — The  Wickes  verti- 
cal water-tube  boiler  is  illustrated  in  Fig.  26.     It  consists  of  a 
large  steam  drum  at  the  top  and  a  smaller  drum,  having  the 
same  diameter,  at  the  bottom.     The  water  tubes  are  vertical 
and  connect  these  two  drums.     The  top  or  steam  drum  is  large 
enough  for  a  man  to  enter  and  stand  upright.     This  makes 
cleaning  the  tubes  easier. 

The  tubes  are  divided  into  two  sets  by  a  tile  baffle  plate 
which  extends  from  the  lower  drum  almost  to  the  bottom 
of  the  upper  one,  thus  directing  the  flue  gases  upward  along 
the  front  set  of  tubes  and  downward  along  the  rear  set  to 
the  smoke  connection  which  is  placed  at  the  lower  end  of  the 
tubes. 

The  circulation  is  upward  in  the  front  set  of  tubes  to  the 
steam  drum  and  downward  in  the  rear  set.  A  baffle  plate 
is  placed  in  the  steam  drum  directly  over  the  ends  of  the 
front  set.  of  tubes.  This  directs  the  current  of  water  across 
the  steam  drum  to  the  entrance  of  the  downcast  tubes  at  the 
rear. 

The  feed  pipe  enters  the  steam  drum  just  over  the  rear  tubes 
and  discharges  downward  into  these  tubes.  By  the  time  the 
feed  water  has  reached  the  lower  ends  of  the  tubes,  it  has  become 
heated  sufficiently  to  cause  it  to  deposit  the  larger  part  of  its 
scale-forming  elements,  and  these,  together  with  the  mud  and 
sediment,  collect  in  the  lower  drum  where  the  water  is  nearly 
quiet.  The  blow-off  pipe  is  connected  to  the  bottom  of  the 
mud  drum. 

The  boiler  is  supported  by  four  lugs  riveted  to  the  mud  drum, 


32 


STEAM  BOILERS 


the  lugs  resting  directly  on  the  foundation,  which  consists  of  a 
circular  masonry  wall. 


FIG.  26. — Wickes  vertical  water-tube  boiler. 

27.  Cahall  Vertical  Water -tube  Boiler.— Fig.  27  show's  a  Cahall 
vertical  water-tube  boiler.  As  in  the  Wickes  boiler,  there  are 
two  drums  connected  by  a  series  of  straight  tubes,  but  in  the 
Cahall  boiler  the  upper  drum  is  in  the  form  of  a  hollow  ring  and  is 
larger  in  diameter  than  the  bottom  drum.  This  gives  the  nest 
of  tubes  a  conical  instead  of  cylindrical  form. 

The  flue  gases  pass  the  length  of  the  boiler  but  once,  rising 
from  the  grate  through  the  nest  of  tubes  directly  to  the  top 
where  they  pass  out  through  the  central  part  of  the  top  drum 
to  the  smoke  connection.  The  flue  gases  are  deflected  across 
the  tubes  by  means  of  baffle  plates  located  in  the  hollow  interior 
of  the  cone  formed  by  the  tubes. 


WATER-TUBE  BOILERS  33 

The  circulation  is  upward  in  the  tubes  to  the  top  drum,  where 
the  steam  is  released  and  the  water  is  carried  to  the  bottom 
drum  by  means  of  a  circulating  pipe  which  connects  the  two 
drums  outside  the  setting.  The  feed  water  enters  the  bottom 
drum  where  the  mud  and  sediment  settles  and  may  be  blown 
out. 


FIG.  27. — Cahall  vertical  water-tube  boiler. 


28.  Rust  Vertical  Water-tube  Boiler.— The  Rust  vertical 
water-tube  boiler  shown  in  Fig.  28  is  somewhat  different  in 
form  from  the  other  vertical  water-tube  boilers  shown.  It  consists 
of  two  horizontal  water  and  steam  drums  at  the  top,  connected 
by  two  nests  of  tubes  to  two  mud  drums  at  the  bottom.  Thus, 
there  is  one  steam  drum  directly  over  each  mud  drum.  The  two 
steam  drums  at  the  top  are  connected  by  two  sets  of  tubes, 


34 


STEAM  BOILERS 


one  connected  below,  and  the  other  above  the  water  line  of 
each  drum.  The  bottom  or  mud  drums  are  also  connected 
by  a  series  of  short  straight  tubes.  A  baffle  wall,  extending 
from  the  mud  drums  nearly  to  the  top  of  the  tubes,  is  built 
between  the  two  sets  of  tubes. 

The  flue  gases  pass  from  the  grate  to  the  front  set  of  tubes 


FIG.  28. — Rust  vertical  water-tube  boiler. 


and  follow  along  these  to  the  top  of  the  baffle  wall,  where  they 
pass  across  to  the  rear  set  of  tubes  and  down  these  to  the  smoke 
connection  at  the  bottom.  A  series  of  baffle  plates  are  placed 
both  on  the  baffle  wall  and  on  the  setting  to  deflect  the  gases 
across  the  tubes  in  their  passage  to  the  smoke  connection. 

The  Rust  boilers  are  made  in  two  forms,  one  of  which  has  an 


WATER-TUBE  BOILERS  35 

extra  row  of  curved  tubes  built  against  each  side  of  the  baffle 
waH;  as  shown  in  Fig.  28,  while  the  other  form  does  not  have 
these  rows  of  tubes.  The  purpose  of  the  extra  rows  of  tubes 
is  to  strengthen  the  baffle  wall  and  also  to  give  additional  heat- 
ing surface. 

The  circulation  of  water  in  the  Rust  boiler  is  up  the  front  set 
of  tubes  to  the  front  steam  drum,  where  the  steam  formed  in 
this  set  of  tubes  is  separated.  The  steam  passes  across  to  the 
rear  steam  drum  through  the  tubes  connecting  the  steam  spaces 
of  the  two  drums,  while  the  water  passes  over  to  the  rear  steam 
drum  through  the  lower  row  of  tubes.  The  water  then  continues 
down  the  rear  set  of  tubes  to  the  rear  mud  drum  and  through 
the  short  connecting  tubes  to  the  front  drum. 

The  feed  water  enters  through  one  end  of  the  rear  steam  drum 
and  is  discharged  downward  into  the  rear  set  of  tubes.  Each 
of  the  bottom  drums  is  provided  with  a  blow-off  for  discharging 
the  mud  and  sediment  that  collects  in  them. 

29.  Comparison  of  Types. — It  is  often  desirable  to  compare 
boilers  of  different  types  in  order  to  determine  which  is  best 
suited  for  certain  conditions.  For  this  purpose  it  is  well  to  know 
something  of  the  advantages  and  disadvantages  of  the  different 
types.  These  are  briefly  stated  here  for  the  three  types,  the 
flue,  the  fire-tube,  and  the  water-tube  types. 


LANCASHIRE  TYPE 

Advantages  Disadvantages 

1.  Simple  in  construction.  1.  Slow  steaming. 

2.  Easily  cleaned  and  examined.        2.  Liability  to  leak  from  unequal 

expansion. 

3.  Large  steam  space.  3.  Great  floor  space  required. 

4.  Not  liable  to  prime.  4.  Specially  skilled  men  required 

for  repairs. 

5.  Reduction  in  pressure  necessary 
after  a  time. 


As  may  be  seen  from  Fig.  2,  the  flue  boiler  is  simple  in  con- 
struction and  is  easily  examined  and  cleaned  since  there  are  but 
few  flues  in  it.  This  boiler  has  a  large  steam  space,  since  the 
shell  is  long  and  is  only  partly  filled  with  water.  On  account 


36  STEAM  BOILERS 

of  the  large  surface  of  the  water  the  boiling  need  not  be  very 
violent  and,  hence,  quite  dry  steam  may  be  obtained. 

Owing  to  the  large  mass  of  water  contained  in  the  shell  it 
takes  considerable  time  to  get  up  steam.  This  boiler  is  not 
well  adapted  to  sudden  large  demands  for  steam  as  the  pressure 
cannot  be  changed  quickly  since  the  entire  mass  of  water  in  the 
boiler  must  have  its  temperature  changed  before  the  pressure 
can  be  changed. 

Since  the  flue  boiler  has  but  little  heating  surface  for  a  given 
size,  it  occupies  a  large  floor  space.  Repairs  are  not  easily  made 
on  it  because  the  repairs  to  this  type  of  boiler  usually  require 
some  riveting,  as  the  flues  are  riveted  to  the  heads,  and  such 
work  cannot  be  done  by  an  unskilled  workman. 

On  account  of  the  weakening  of  the  shell  by  corrosion  and 
pitting  caused  by  impure  feed  water,  it  becomes  necessary  after 
a  time  to  reduce  the  pressure  carried  by  a  flue  boiler. 


FIRE-TUBE  TYPE 

Advantages  Disadvantages 

1.  Small  floor  space  required.  1.  Small  steam  space,  hence,  pres- 

2.  Quick  steaming.  sure  liable  to  fluctuate. 

3.  Ruptured  tubes  easily  replaced.     2.  Not  easily  cleaned  or  examined. 

3.  Liable  to  leak  at  ends  of  tubes, 

at  stays,   and   at   corners  of 
fire  box. 

4.  Reduction  of  pressure  necessary 

in  time. 

Most  of  the  heating  surface  in  a  fire-tube  boiler  is  in  the  large 
number  of  small  tubes  which  are  grouped  closely  together. 
Thus  a  large  amount  of  heating  surface  is  placed  within  a  small 
amount  of  floor  space.  The  tubes  divide  up  the  mass  of  water 
in  the  boiler  and  distribute  the  heat  throughout  it,  thus  making 
it  possible  for  steam  to  be  raised  or  the  pressure  to  be  changed 
quickly  to  respond  to  changes  in  the  load.  As  the  flues  are 
simply  expanded  into  the  tube  sheets,  it  is  not  a  difficult  matter 
to  remove  one  when  burned,  and  replace  it  by  a  new  one. 

Since  so  large  a  portion  of  the  boiler  is  occupied  by  the  tubes 
and  since  the  water  line  must  be  carried  above  the  top  row  of 
them,  there  is  a  comparatively  small  steam  space.  Consequently, 


WATER-TUBE  BOILERS  37 

when  a  sudden  load  is  thrown  on  an  engine,  the  steam  supply 
may  not  be  sufficient  to  meet  the  demand  and  the  pressure  may 
fall. 

On  account  of  the  tubes  being  placed  very  close  together  and 
the  rows  staggered,  it  is  difficult  to  clean  or  examine  them.  For 
this  reason,  only  very  good  feed  water  should  be  used  with  this 
type  of  boiler.  But  even  then  there  will  be  a  certain  amount  of 
corrosion,  which  will  weaken  the  shell  in  time  and  make  it 
necessary  to  reduce  the  pressure.  The  liability  to  leak  is  a 
natural  consequence  of  the  large  number  of  tubes  and  seams. 

WATER-TUBE  TYPE 

Advantages  Disadvantages 

1.  Rapid  steaming.  1.  Small  steam  space. 

2.  Safety.  2.  Not  easily  cleaned. 

3.  Small  floor  space  required.  3.  Liable  to  prime. 

4.  Repairs  easily  made. 

5.  Reduction  of  pressure  not  neces- 

sary in  time. 

6.  Large  capacity  for  small  weight 

and  size. 

In  the  water-tube  boiler,  the  water  is  divided  into  a  large 
number  of  small  masses  contained  in  the  tubes  and,  as  the  surface 
of  these  tubes  comprises  the  larger  part  of  the  heating  surface, 
the  heat  is  easily  and  quickly  transmitted  to  the  water.  There- 
fore, the  boiler  is  a  rapid  steamer  and  fluctuations  in  load  are 
easily  taken  care  of,  but  as  the  steam  drum  has  but  small  capacity 
the  pressure  is  liable  to  fluctuate  unless  watched  closely. 

Another  result  of  having  the  larger  part  of  the  water  contained 
in  the  tubes  is  the  increased  safety  against  explosion.  The  tubes 
are  small  in  diameter,  and  their  walls  comparatively  thick,  so 
they  are  quite  strong  and  able  to  withstand  a  high  pressure. 
Even  should  one  of  them  burst,  the  amount  of  water  brought 
into  action  is  small  and  no  very  serious  explosion  can  result. 

About  the  only  part  of  a  water-tube  boiler  that  is  liable  to 
give  out  is  the  tubes,  especially  those  directly  over  the  fire.  As 
these  are  simply  expanded  into  the  headers,  they  may  easily  be 
replaced  by  new  ones,  and  the  strength  of  the  boiler  maintained 
at  its  original  value.  Consequently,  it  is  not  necessary  to  reduce 
the  pressure  after  the  boiler  has  been  in  use  for  a  time. 

4 


38  STEAM  BOILERS 

By  the  statement  that  the  water-tube  boiler  is  not  easily 
cleaned  is  meant  not  so  much  that  there  is  any  special  difficulty 
in  getting  at  the  surfaces  of  the  tubes  but  rather  that  it  is  con- 
siderable trouble  to  clean  them  on  account  of  the  large  number 
of  handhole  covers  that  have  to  be  removed,  cleaned,  and 
replaced.  The  liability  of  this  type  of  boiler  to  prime  is  a  natural 
consequence  of  the  comparatively  small  steam  drum  and  the 
small  surface  for  the  liberation  of  the  steam. 


CHAPTER  III 
BOILER  CALCULATIONS 

30.  Boiler  Horse-power. — The  term  " horse-power"  or  "boiler 
horse-power"  (abbreviated  boiler  h.p.)  is  generally  used  to 
express  the  size  or  capacity  of  a  boiler.  Strictly  speaking, 
the  use  of  the  term  horse-power  in  this  connection  is  not  correct, 
since  the  word  horse-power  indicates  a  rate  of  doing  work, 
whereas  a  boiler  does  no  work  in  the  ordinary  sense  in  which  we 
speak  of  work.  It  is  the  engine  that  does  the  work  in  a  power 
plant,  and  the  boiler  merely  supplies  the  steam  to  the  engine. 
However,  the  term  horse-power  has  become  so  generally 
used  to  designate  the  sizes  of  boilers  that  it  is  probable  its  use 
will  be  continued  always.  No  confusion  need  result,  however, 
if  the  meaning  of  the  term  as  applied  to  boilers  is  throughly 
understood.  It  must  be  kept  in  mind,  however,  that  there  is 
no  definite  relation  between  the  horse-power  of  an  engine  and 
the  horse-power  of  a  boiler. 

The  manufacturers  of  boilers  generally  rate  their  boilers  on  the 
basis  of  the  number  of  square  feet  of  heating  surface  which  they 
contain.  For  water-tube  boilers,  10  sq.  ft.  of  heating  surface 
are  considered  sufficient  for  one  horse-power.  Thus  a  water- 
tube  boiler  containing  1000  sq.  ft.  of  heating  surface  would  be 
rated  as  a  100  horse-power  boiler.  For  Scotch  marine  boilers 
8  sq.  ft.,  for  fire-tube  boilers  10  to  12£  and  for  flue  boilers  12 
to  15  sq.  ft.  are  allotted  to  each  horse-power. 

It  can  be  readily  seen  that  this  method  of  rating  boilers  is 
not  very  satisfactory  from  the  standpoint  of  the  purchaser,  as 
a  boiler  from  one  maker  may  have  its  heating  surface  more 
advantageously  arranged  than  that  of  another  which  has  the 
same  number  of  square  feet  of  heating  surface.  Yet,  according 
to  this  method  of  rating,  they  would  both  be  rated  at  the  same 
horse-power.  It  is  well  known  that  all  the  heating  surface  in  a 
boiler  is  not  equally  effective,  but  that  the  surface  immediately 
surrounding  the  furnace  transmits  a  much  larger  proportion  of 
heat  than  the  surface  near  the  smoke  connection. 
5  39 


40  STEAM  BOILERS 

A  much  more  satisfactory  method  of  rating  boilers  is  upon  the 
amount  of  water  which  they  will  evaporate  under  ordinary  run- 
ning conditions.  This  is  a  reasonable  way  to  rate  a  boiler,  since 
its  duty  consists  in  evaporating  water.  A  method  of  rating 
boilers  upon  this  basis  will  be  taken  up  in  a  later  chapter,  after 
the  properties  of  steam  have  been  studied. 

31.  Heating  Surface. — Tn  measuring  the  heating  surface  of 
boilers  it  is  customary  for  manufacturers  to  base  their  measure- 
ments on  the  outside  diameter  of  the  tubes  and  flues  rather  than 
on  the  inside  diameter.  This,  of  course,  gives  a  greater  area  than 
if  the  inside  diameter  was  used.  They  give  as  reasons  for  doing 
this  that  it  is  simpler,  since  boiler  tubes  are  catalogued  and  ordered 
according  to  their  outside  diameters;  that  there  is  no  need  of 
being  so  very  accurate,  since  the  heat  transmitting  ability  of  the 
tube  varies  for  different  locations  of  the  heating  surface  and 
with  the  thickness  of  the  metal;  and  that  this  method  is  better 
for  making  comparisons. 

Many  engineers  argue  that  the  surface  whjch  receives  the  heat 
should  be  the  measure  of  the  heating  surface,  since  this  surface 
is  the  technically  correct  heating  surface.  This,  of  course, 
results  in  the  outside  diameter  of  water-tube  and  the  inside 
diameter  of  fire-tube  boilers  being  taken.  The  American 
Society  of  Mechanical  Engineers  favors  the  latter  plan  of  com- 
puting the  heating  surface;  that  is,  taking  the  surface  area  of 
shells,  tubes,  furnaces,  and  fire  boxes  in  contact  with  the  fire  or 
hot  gases. 

All  of  the  surface  in  contact  with  fire  or  hot  gases  on  one  side 
and  water  on  the  other  side  is  called  heating  surface  and  all  the 
surface  which  has  fire  or  hot  gases  on  one  side  and  steam  on  the 
other  side  is  called  superheating  surface.  Water-heating  surface 
is  very  effective  in  transmitting  heat,  while  the  heat  trans- 
mission through  superheating  surface  is  very  slow,  and  for  this 
reason  the  superheating  surface  should  not  be  counted  in  as 
heating  surface  in  rating  a  boiler.  These  two  surfaces  should  be 
computed  and  noted  separately  in  giving  the  data  concerning  a 
boiler  test.  The  surface  below  the  line  of  the  grates,  to  which  the 
fire  does  not  have  access,  should  be  counted,  nor  any  surface  that 
is  covered  by  brickwork.  Only  three-eighths  of  the  shell  of  fire- 
tube  boilers  should  be  counted  as  heating  surface  when  the  side 
walls  come  straight  up  tangent  to  the  shell,  because  the  sharp 
corners  between  the  shell  and  the  brickwork  form  a  dead  space 


BOILER  CALCULATIONS  41 

in  which  the  hot  gases  cannot  circulate.  If  the  brickwork  is 
corbeled  off  from  the  shell  the  full  half  of  the  shell  may  be 
counted  as  heating  surface.  As  an  aid  in  calculating  the  heat- 
ing surface  in  boiler  tubes,  the  following  table  of  boiler  tube 
sizes  is  given: 

To  illustrate  the  method  of  calculating  heating  surface,  and 
from  it  the  horse-power  of  a  boiler,  consider  the  overhung  fire- 
tube  boiler  shown  in  Fig.  4.  This  boiler  has  34  three-inch  tubes 
and  is  14  ft.  long,  the  diameter  of  the  shell  being  42  in.  Let  us 
consider  that  the  brickwork  of  the  setting  will  be  brought  up 
close  to  the  shell,  so  that  only  three-eighths  of  the  surface  of  the 
shell  will  be  effective  heating  surface. 

The  circumference  of  a  circle  =3. 1416  times  the  diameter, 
therefore,  the  circumference  of  the  shell  =3. 1416  Xf I  =  3.1416 
X3. 5-11.00  ft. 

Surface  of  the  shell  =  14  X  10.99  =  154  sq.  ft. 

As  only  three-eighths  of  this  is  effective,  the  effective  heating 
surface  of  the  shell  is  3/8X153.9  =  57.8  sq.  ft. 

Internal  circumference  of  one  tube  =  3. 1416X2. 782— 8.74  in. 
(See  table  on  page  42.) 

Internal  area  of  one  tube -14X12X8.74 -1468. 3  sq.  in. 

Internal  area  of  34  tubes -34X1468.3  =  49,922  sq.  in. 

Area  of  tubes  in  square  feet  -49,922  -s- 144-346.6  sq.  ft. 

Total  heating  surf  ace -57.8 +346.6  =404.4  sq.  ft. 

If  this  boiler  was  rated  on  the  basis  of  10  sq.  ft.  of  heating 
surface  to  each  horse-power,  it  would  have  404. 4 -=-10  =40. 44 
boiler  h.p.,  while,  if  it  was  rated  on  the  basis  of  12  sq.  ft.  to 
each  horse-power,  it  would  have  404.4  -5- 12—  33.7  boiler  h.p. 

The  area  of  the  tube  sheets  need  not  be  counted  in  the  heating 
surface  as  their  area  is  small  and  the  surface  not  very  effective 
in  transferring  heat. 

In  calculating  the  heating  surface  of  a  water-tube  boiler,  the 
external  surface  of  the  tubes  must  be  considered.  Take  for 
example  the  Murray  water-tube  boiler  shown  in  Fig.  21,  which 
has  67  tubes  3J  in.  in  diameter  and  16  ft.  long.  The  headers 
are  64  in.  wide  and  42  in.  high.  Consider  the  steam  drum  as 
having  a  diameter  of  30  in.,  with  the  hot  gases  in  contact  with  it 
for  a  length  of  16  ft.,  and  with  one-half  of  its  drum  surface  effect- 
ive heating  surface. 

The  circumference  of  each  tube  is  3.1416X3,5-  11  in.,  and 
its  surface  is  11x16x12-2112  sq.  in. 


42 


STEAM  BOILERS 


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BOILER  CALCULATIONS 


43 


67  tubes  will  have  an  area  of  67X2112  =  141,504  sq.  in. 
141,504-144  =  982.7  sq.  ft. 

The  circumference  of  the  drum  is  3.1416X30  =  94.25  in.  and 
its  surface  is  16X94.25X12  =  18,096  sq.  in.     Since  one-half  of 
this  area  is  heating  surface,  this  will  amount  to 
18,096 -2  =  9, 048  sq.  in. 
9048  + 144  =  62.8  sq.  ft. 

The  headers  have  a  total  area  each  of  64x42=2688  sq.  in. 
The  cross  sectional  area  of  each  tube  is  .7854X3.52  =  9.62  sq.  in. 
and  the  area  of  all  tubes  is  67X9.62  =  645  sq.  in.  The  net  area 
of  each  header  is 

2688-645=2043  sq.  in. 
2043 -144  =  14. 19  sq.ft. 

or  in  two  headers  there  will  be  2  X 14. 19  =28. 4  sq.  ft. 
This  gives  a  total  heating  surface  of  982.7  +  62.8  +  28.4  =  1074 
sq.  ft. 

From  the  small  part  of  the  total  heating  surface  which  the 
headers  contain  it  will  be  seen  that  the  area  of  the  headers  may 
well  be  neglected.  Leaving  this  out  would  give  a  total  heating 
surface  of  1045.5  sq.  ft.,  which,  on  a  basis  of  10  sq.  ft.  per  horse- 
power would  give  104.6  boiler  h.p.  This  boiler  would  probably 
be  rated  as  a  100  h.p.;  boiler. 

The  following  table  of  standard  steam-boiler  measurements  is 
inserted  as  an  aid  in  determining  quickly  the  horse-power  of  a 
boiler  of  standard  size.  This  table  applies  only  to  return  fire- 
tube  boilers. 

STANDARD  STEAM-BOILER  MEASUREMENTS 
Based  on  12  sq.  ft.  of  heating  surface  to  a  horse-power 


Size 

Thickness 

Boiler  with  han  dholes 

Boiler  with  manholes 

Tubes 

Heat 
surf, 
sq.  ft. 

Horse- 
power 

Tubes 

Heat 
surf, 
sq.  ft. 

Horse- 
power 

Dia. 

Length 

Shell 

Heads 

No. 

Dia. 

No. 

Dia. 

30 
30 

36 
36 

6 

8 

8 
10 

i 
i 

i 
1 

I 

i 

i 
i 

19 
19 
(    38 
\     28 
I    25 
f    38 
28 
I    25 

2i 
2i 
2i 
3 
3* 
2* 
3 
3i 

106 
141 
256 
226 
234 
311 
283 
292 

9 
12 
21 
19 
20 
26 
24 
24 

44 


STEAM  BOILERS 


STANDARD    STEAM-BOILER  MEASUREMENTS— Continued 
Based  on  12  sq.  ft.  of  heating  surface  to  a  horse-power 


Size 

Thickness 

Boiler  with  handholes 

Boiler  with  manholes 

Tubes 

Heat 

surf. 
sq.  ft. 

Horse- 
power 

Tubes 

Heat 
surf, 
sq.  ft. 

Horse- 
power 

Dia. 

Length 

Shell 

Heads 

No. 

Dia. 

No. 

Dia. 

42 

10 

i 

i 

38 
34 

3 

34 

372 

385 

31 
32 

38 

3 

446 

37 

42 

12 

1 

f 

34 

34 

462 

39 

38 

3 

520 

43 

42 

14 

1 

•f 

34 

34 

539 

45 

42 

16 

1 

f 

38 
34 

O  J 

3 

34 

595 
616 

50 
51 

48 

3 

544 

45 

44 

12 

* 

* 

< 

38 

34 

510 

43 

48 

3 

635 

53 

44 

14 

J 

1 

28 

34 

491 

41 

58 

O  2 

3 

647 

54 

50 

3 

572 

48 

48 

12 

A 

i7<$ 

50 

34 

651 

54 

34 

34 

475 

40 

A  O 

1  A 

- 

_ 

58 

3 

755 

63 

50 

3 

667 

55 

48 

Irt 

IB 

IS 

50 

34 

759 

63 

34 

34 

547 

46 

58 

3 

862 

72 

50 

3 

762 

64 

48 

16 

A 

i7» 

50 

34 

867 

72 

34 

34 

633 

53 

58 

3 

970 

81 

50 

3 

857 

71 

48 

18 

& 

" 

50 

34 

976 

81 

34 

34 

712 

59 

71 

3 

912 

76 

59 

3 

780 

65 

54 

14 

A 

4 

56 

34 

851 

71 

48 

34 

748 

62 

43 

4 

763 

64 

40 

4 

719 

60 

71 

3 

1042 

87 

59 

3 

891 

74 

54 

16 

A 

| 

56 

34 

972 

81 

48 

34 

855 

71 

43 

4 

802 

67 

40 

4 

821 

68 

71 

3 

1173 

98 

59 

3 

1003 

84 

54 

18 

A 

4 

56 

34 

1094 

91 

48 

34 

962 

80 

43 

4 

980 

82 

40 

4 

924 

77 

71 

34 

907 

75 

56 

34 

742 

62 

60 

12 

A 

4 

54 

4 

804 

67 

46 

4 

704 

59 

43 

44 

733 

61 

36 

44 

634 

53 

71 

34 

1058 

88 

56 

34 

865 

72 

60 

14 

A 

} 

CA 

4 

938 

78 

46 

4 

821 

68 

43 

44 

855 

71 

36 

44 

740 

62 

* 

''  71 

34 

1209 

101 

56 

34 

989 

82 

60 

16 

A 

4 

• 

54 

4 

1073 

89 

46 

4 

939 

78 

1  43 

44 

978 

82 

36 

44 

846 

71 

f  71 

34 

1360 

113 

56 

34 

1113 

93 

60 

18 

A 

} 

54 

4 

1207 

101 

46 

4 

1056 

88 

{  43 

44 

1100 

92 

36 

44 

952 

79 

90 

34 

1504 

125 

84 

34 

1416 

118 

66 

16 

f 

4 

68 

4 

1324 

110 

56 

4 

1122 

94 

56 

44 

1239 

103 

46 

44 

1051 

88 

90 

34 

1692 

141 

84 

34 

1593 

133 

66 

18 

£ 

I 

68 

4 

1489 

124 

56 

4 

1263 

105 

56 

44 

1394 

116 

46 

44 

1113 

93 

{108 

34 

1785 

149 

98 

34 

1638 

137 

72 

16 

f 

£ 

82 

4 

1575 

131 

72 

4 

1407 

117 

64 

44 

1407 

117 

60 

44 

1331 

111 

(108 

34 

2008 

167 

98 

34 

1843 

154 

72 

18 

f 

4 

82 

4 

1772 

148 

72 

4 

1584 

132 

64 

44 

1583 

132 

60 

44 

1498 

125 

BOILER  CALCULATIONS 


45 


32.  Corrugated  Flues. — Many  flue  boilers  have  the  furnace 
flues  made  of  corrugated  sheets  in  order  to  give  them  greater 
strength  to  resist  the  crushing  pressure  to  which  they  are  sub- 
jected, and  also  to  allow  them  to  expand  and  contract  without 
disturbing  other  parts  of  the  boiler.  The  principal  types  of 
corrugated  flues  are  illustrated  in  Figs.  29  and  30.  The  first 
is  known  as  the  Morison  suspension  flue  and  the  second  as  the 
Fox  corrugated  flue. 


2    I 


FIG.  29. — Morison  suspension  flue.      FIG.  30. — Fox  corrugated  flue. 

Owing  to  the  peculiar  shape  of  the  surface  of  these  flues  it  is 
rather  difficult  to  compute  the  area  exactly.  A  simple  method 
of  estimating  the  heating  surface  of  one  of  these  tubes  is  to  con- 
sider it  as  being  a  straight  cylinder  with  a  diameter  equal  to 
the  mean,  or  average  diameter  of  the  corrugated  flue;  and  then 
to  add  to  the  surface  of  this  cylinder  14^  per  cent  of]  its  sur- 
face for  the  Morison  flue  or  9^  per  cent  for  the  Fox  flue. 

To  illustrate  this,  suppose  we  wish  to  find  the  heating  surface 
contained  in  a  Morison  suspension  furnace  flue  which  has  a 
maximum  diameter  of  39J  in.  and  a  minimum  diameter  of 

36  in.  and  is  9  ft.  3  in.  long.     The  mean  diameter  is 


39J  +  36 


n. 


Compute  the  area  of  a  cylindrical  flue  having  a  diameter  of 
in.  and  a  length  of  9  ft.  3  in.  The  circumference  is 
3.1416 X37!9F  =  118  in.  The  length  is  9  ft.  3  in.  =  111  in. 
Therefore  the  surface  is  118  X  111  - 13,098  sq.  in.  13,098  * 144  = 
91  sq.  ft.  Adding  14J-  per  cent  to  this  gives  91 +  (.145X91)  = 
91  +  13.2  =  104.2  sq.  ft.  as  the  heating  surface  of  the  flue. 


46  STEAM  BOILERS 

If  the  flue  had  been  of  the  Fox  corrugated  type  we  would 
calculate  its  surface  in  the  same  way  except  that  instead  of  add- 
ing 14J  per  cent,  we  would  add  9T%-  per  cent;  that  is,  its  sur- 
face, considered  as  a  cylinder  having  a  diameter  of  37T9e-  in., 
would  be  91  sq.  ft.  as  before.  Adding  9^  per  cent  to  this 
gives  91  +  (.094X91)  =91+8.55  =  99.55  sq.  ft.  as  the  heating 
surface  of  a  Fox  flue  of  the  same  dimensions. 

33.  Strength  of  Shell. — The  force  tending  to  burst  a  boiler 
shell  may  be  computed  from  the  formula 

pD=2St  (1) 

in  which  p  is  the  pressure  per  square  inch 

D  is  the  diameter  of  shell  in  inches 
S  is  the  stress  in  the  metal  per  square  inch 
t  is  the  thickness  of  the  shell  in  inches. 
If  there  are  any  riveted  joints  and  the  efficiency  of  the  joint 

is  e,  the  above  formula  will  have  to  be  modified,  and  it  will  then 

become 

pD=2Ste  (2) 

The  efficiency  of  a  joint  is  the  relation  of  the  strength  of  the 
joint  to  the  strength  of  the  solid  plate. 

The  pressure  per  square  inch  required  to  burst  the  boiler 
will  then  be 

2Ste 

P=~^  (3) 

in  which  S  is  the  breaking  strength  per  square  inch  of  metal  in 
the  shell. 

Example:  What  pressure  will  burst  a  cylindrical  boiler  shell 
72  in.  in  diameter,  if  the  metal  is  1/4  in.  thick  and  has  a  strength 
of  60,000  Ib.  per  square  inch,  and  if  it  has  a  riveted  joint  whose 
efficiency  is  70  per  cent? 

2 X 60,000 X. 25  X- 70 

Solution:  p  =  —  -  =292lb. 

7 2i 

The  thickness  of  the  shell  to  withstand  a  given  pressure  may 
be  found  from  the  formula 


BOILER  CALCULATIONS  47 

Example:  What  should  be  the  thickness  of  the  shell  in  the 
above  example  if  it  is  to  withstand  a  pressure  of  500  Ib.  per 
square  inch? 

500X72 


This  boiler  would  presumably  burst  at  a  pressure  of  500  Ib. 

In  designing  boilers  it  is  necessary  to  make  them  stronger  than 
the  above  formulas  would  indicate,  and  the  number  of  times 
stronger  that  they  are  made  is  called  the  factor  of  safety.  It  is 
common  practice  to  make  the  factor  of  safety  for  steam  boilers 
from  4  to  6;  that  is,  the  boiler  is  made  from  four  to  six  times 
as  strong  as  necessary  to  actually  withstand  the  pressure  which 
it  is  to  carry.  When  the  factor  of  safety  is  known,  the  formula 
for  strength  becomes 

pDf=2Ste  (5) 


where  /  is  the  factor  of  safety. 

The  pressure  which  a  boiler  should  carry  then  becomes 

2Ste 


(6) 


And  the  thickness  of  shell  to  withstand  any  pressure  will  be 

t-&£-  m 

"  2Se 

Example  :  What  should  be  the  thickness  of  the  shell  of  a  60-in. 
boiler  which  is  to  carry  150  Ib.  steam  pressure,  if  the  boiler  is 
made  of  metal  having  a  strength  of  60,000  Ib.  per  square  inch 
and  having  riveted  joints  with  an  efficiency  of  75  per  cent,  a 
factor  of  safety  of  5  being  allowed? 

„  ,  i-  150X60X5 

Solution:  t  =  =  0-5  m' 


By  the  Efficiency  of  a  Riveted  Joint  is  meant  the  ratio  of  the 
strength  of  the  riveted  joint  to  the  strength  of  the  solid  plate  of 
metal. 

^rc  -  Strength  of  joint 

Efficiency  =  zr       zrc—F-Vi 
Strength  of  plate 

The  Hartford  Steam  Boiler  Inspection  and  Insurance  Com- 


48 


STEAM  BOILERS 


pany  have  designed  and  recommended  a  number  of  riveted 
joints,  and,  as  these  include  most  of  the  joints  used  in  boiler 
construction,  the  following  table  is  given  showing  the  dimen- 
sions of  these  joints  together  with  their  efficiencies.  The  ulti- 
mate tensile  strength  refers  to  the  boiler  plate,  and  the  ulti- 
mate shearing  strength  refers  to  the  rivets,  as  the  plates  will 
fail  by  tension  while  the  rivets  will  fail  by  being  sheared  off. 


PROPORTIONS    OF   RfVETED    JOINTS 


Type  of  Joint 


Position  of  Joint      t       t1 


d'      d 


v"      v' 


Lontjrt-udinal 
seam.  Double- 
riveted   l 
joint. 


Single  -riveted 

girth  seam 

used  with 

above 


Longitudinal 

seam.  Triple- 

riveted  la{> 

joint 


Single  -  riveted 

girth   seam 

used  with 

above 


Longitudinal 
seam.  Tri  pie- 
iveted  butt  joint 
with  double  welt 


Single-  riveted 

girth  seam 

U6ed  with 

above 


h? 


ITS 


2ft 


677 


545 
49/4 

(3!  490 
46.6 
lg  44* 


770 
76.C 
75.0 
750 
74.6 


£450 
41.9 
41.2 
4Z.O 
395 


88.0 
85.0 
i86.0 


'si 


44.6 
43.8 
44.0 
44.2 


Note  :- 


C  Ultimate  tensile  strength  of  plate  taken 
^  shearing     "         "  rivets 


as  6O.OOO  Ibs.  per  sq.  in. 
11   38,000 


Formulas  Nos.  1  to  7  in  this  chapter  apply  only  to  the  strength 
of  shell  in  a  longitudinal  direction,  or  along  the  sides  of  the  shell. 
To  calculate  the  strength  of  shell  against  bursting  around  the 
girth,  the  formula  for  the  safe  working  pressure  is 


P  = 


4_Ste 

w 


(8) 


BOILER  CALCULATIONS  49 

In  this  formula  e  applies  to  efficiency  of  the  girth  joint.  It  will 
be  seen  by  comparing  formulas  3  and  8  that,  for  the  same  pres- 
sure, diameter,  thickness,  and  factor  of  safety,  the  efficiency  of 
the  girth  joint  of  a  boiler  need  be  only  one-half  that  of  the 
longitudinal  joint.  This  explains  why  the  longitudinal  joints 
are  always  made  the  stronger  of  the  two. 

To  illustrate  the  use  of  these  formulas  and  their  relations  to 
each  other,  let  us  take  the  following  example: 

Example:  Suppose  we  wish  to  calculate  the,  safe  working 
pressure  for  a  fire-tube  boiler  60  in.  in  diameter,  16  ft.  long, 
having  a  shell  1/2  in.  thick.  The  longitudinal  seam  is  a  triple- 
riveted  butt  joint  with  double  welt,  with  size  of  rivets  and  spacing 
according  to  the  table  of  riveted  joints.  The  girth  seam  is  a 
single  -riveted  lap  joint  with  15/16-in.  rivets  spaced  2\  in.  apart. 
The  strength  of  the  metal  used  in  the  plates  is  60,000  Ib.  per 
square  inch.  Use  a  factor  of  safety  of  5. 

Solution:  By  referring  to  the  table  of  riveted  joints  it  will  be 
seen  that  the  efficiency  of  the  girth  joint  is  44.2  per  cent.,  there- 
fore the  safe  working  pressure,  so  far  as  the  boiler  bursting 
around  the  girth  is  concerned,  is 

4Ste     4X60,OOOX0.5X.442 
p  =  -gyr  =  -  60  X5~        -  =  1  77  Ib.  per  square  inch. 

The  efficiency  of  the  longitudinal  riveted  seam  is,  from  the 
table,  86.6  per  cent;  therefore,  the  boiler  can  stand  a  safe  working 
pressure,  against  bursting  along  the  side,  of 

2  Ste     2X60,OOOX0.5X.866  .     , 

p  =  -jy-  =  6Qx5—  =  1  73  Ib.  per  square  inch. 

This  latter  value  (173  Ib.)  should  be  the  maximum  pressure 
allowed  in  the  boiler. 

34.  Strength  of  Furnace  Flues.  —  The  safe  working  pressure 
that  may  be  allowed  on  corrugated  flues,  such  as  the  Morison  and 
the  Fox,  may  be  calculated  from  the  following  formula: 

14,000* 


in  which  p  =  safe  working  pressure  in  pounds  per  square  inch 

t  =  thickness  of  metal  in  inches 
and          D  =  outside  diameter  of  flue  in  inches. 
The  diameter  of  the  flue  should  be  measured  at  the  bottom  of  the 
corrugations,  thus  giving  the  smallest  outside  diameter. 


50  STEAM  BOILERS 

Example :  What  safe  working  pressure  may  be  allowed  on  the 
Morison  corrugated  flue  shown  in  Fig.  29,  if  the  outside  -diameter 
is  37  in.  and  the  thickness  of  the  metal  is  .5  in.? 

14,000*     14,OOOX.5 

Solution:  p  = =r — ==  —  1—&j =189  pounds  per  square  inch. 

D  o7 

35.  Riveting. — As  riveted  joints  are  the  weakest  points  about 
a  boiler  and  as  they  are  likely  to  leak  unless  carefully  made,  the 
greatest  care  should  be  exercised  in  designing  the  joints  and  in 
doing  the  riveting. 

Rivets  are  made  of  extra  soft  steel  and  can  be  bought  in  various 
lengths  and  sizes,  with  one  head  already  formed.  They  can  be 
bought  in  three  different  styles  of  heads — button,  cone,  and 
countersunk.  The  rounded  heads  in  Fig.  34  are  button  heads, 
while  the  pan-shaped  heads  in  the  same  figure  are  cone  heads, 
being  in  reality  only  a  part,  or  frustum  of  a  cone.  Countersunk 
heads  are  set  into  the  plate  so  as  to  leave  a  smooth,  or  flush  sur- 
face. Countersunk  rivets  should  never  be  used,  if  possible  to 
avoid  it,  as  the  countersinking  weakens  the  plate  and  the  counter- 
sunk head  will  pull  through  the  plate  rather  easily. 

Rivets  are  designated  as  to  size  by  the  diameter  of  the  shank 
or  body  and  by  the  length  under  the  head,  except  that  counter- 
sunk rivets  are  known  by  the  length  to  the  top  of  the  head. 

The  rivet  holes  in  the  plates  are  made  1/16  in.  larger  than  the 
diameter  of  the  rivet,  so  the  rivet  may  be  inserted  easily  while 
hot.  The  holes  are  either  punched,  or  drille'd,  or  punched  and 
reamed.  If  the  plate  is  thin  and  of  wrought  iron  or  very  soft 
steel,  it  may  be  punched  without  greatly  injuring  the  metal. 
Ordinary  boiler  steel,  especially  the  harder  grades,  is  injured  by 
punching,  and  this  method  of  making  the  holes  should  never 
be  allowed  for  power  boilers.  The  injury  by  punching  is  not 
visible  to  the  eye  and  all  the  more  care  should  be  taken  to  prevent 
the  use  of  punched  holes.  Drilling  is  more  accurate  than 
punching,  but  it  is  slower  and  costs  more.  When  the  holes  are 
drilled,  the  sharp  edges  left  by  the  drill  should  be  removed  to 
prevent  them  from  cutting  the  rivet.  In  drilling  plates,  it  is 
best  to  bend  them  to  shape  and  then  clamp  them  together, 
when  they  may  be  drilled  by  a  radial  drill. 

Sometimes  the  holes  are  punched  to  a  smaller  size  than  the 
rivet  and  then  reamed  to  the  proper  size.  When  this  is  done,  at 
least  1/16  in.  of  metal  should  be  reamed  off,  in  order  to  remove 


BOILER  CALCULATIONS 


51 


the  metal  that  is  injured  by  the  punching  process.  When 
properly  done,  punching  and  reaming  gives  a  very  satisfactory 
joint  and  is  cheaper  than  drilling. 

When  plates  are  punched,  the  end  of  the  punch  should  be 
concave  and  a  little  larger  than  its  shank,  in  order  to  secure 
a  clean  cut.  The  hole  in  the  die  is  made  slightly  larger  than  the 
punch,  to  make  the  punching  action  easier.  This  gives  a  hole 


FIG.  31. 

of  slightly  conical  shape  (see  Fig.  31).  When  the  plates  are  put 
together,  the  small  ends  of  the  holes  in  the  two  plates  should  be 
placed  together  as  shown  in  Fig.  31  at  the  left.  The  bulging  of 
the  rivet  will  then  press  the  plates  closer  together;  otherwise,  the 
plates  will  be  forced  apart  by  the  rivet  as  shown  by  the  right- 
hand  rivet  in  Fig.  31. 

Plates  to  be  riveted  should  be  champfered  or  planed  off  on  the 
edge,  as  in  Figs.  32  and  34,  and  after  the  rivets  are  driven  the 
joint  should  be  carefully  caulked  with  a  round-pointed  caulking 
tool.  A  sharp-pointed  tool  should  never  be  used  as  it  is  liable 


BAD 


GOOD 


FIG.  32. 


to  form  a  groove  which  will  increase  rapidly  by  corrosion.     An 
example  of  good  and  bad  caulking  is  shown  in  Fig.  32. 

In  riveting  a  joint,  the  plates  should  be  firmly  clamped  or 
bolted  together.  The  rivets  are  heated  and  inserted  in  the  holes 
with  the  heads  on  the  inside.  A  head  is  then  formed  on  the 
other  end  from  the  stock  of  the  rivet  which  protrudes  through 
the  hole.  The  outer  heads  are  usually  formed  by  machinery, 
though  occasionally  hand  riveting  is  necessary. 


52  STEAM  BOILERS 

Machine  riveting  is  better  than  hand  riveting,  as  the  pressure 
forces  the  shank  to  fill  the  hole  in  the  plates  completely.  Rivet- 
ing machines  are  operated  by  gearing,  water,  pressure,  steam,  or 
air.  The  hydraulic  machines  give  better  results,  as  the  force  is 
applied  to  the  rivets  more  steadily,  causing  them  to  swell 
gradually  and  fill  the  hole  completely.  With  hydraulic,  steam, 
or  air  machines,  the  pressure  may  be  maintained  on  the  rivet 
until  it  has  cooled  sufficiently  to  prevent  stretching  the  shank 
by  the  springing  apart  of  the  plates,  which  might  occur  if  the 
pressure  be  removed  while  the  shank  is  hot.  A  pressure  of  60 
tons  is  considered  sufficient  for  even  the  largest  sizes  of  rivets 
used  in  boiler  work. 

In  certain  parts  of  boilers  where  space  is  small,  and  also  in 
patching,  hand  riveting  becomes  necessary.  The  comparatively 
light  blows  of  a  riveting  hammer  affect  but  a  small  portion  of 


FIG.  33. 

the  metal  of  a  rivet,  and  unless  the  rivet  is  at  the  proper  tem- 
perature and  is  driven  carefully,  there  is  danger  of  forming  the 
head  without  upsetting  the  shank  to  fill  the  hole  in  the  plate. 
This  condition  results  in  a  weak  joint,  as  the  holding  powers  of 
the  rivets  will  then  depend  only  on  the  grip  of  the  heads  on  the 
plates,  and  the  strength  of  the  shank  is  not  utilized.  Fig.  33 
shows  another  defect  which  may  result  from  hand  riveting. 
This  shows  an  imperfectly  formed  head,  that  is,  one  which  is 
centered  to  one  side  of  the  center  lines  of  the  shank,  resulting 
in  a  loss  of  a  part  of  the  holding  power  of  the  head. 

Steel  rivets  should  be  heated  uniformly  throughout  their 
entire  length  and  not  merely  at  the  point,  as  is  sometimes  done 
with  iron  rivets.  This  is  important  since  most  of  the  rivets  now 
used  are  made  of  steel.  As  steel  is  easily  burned,  rivets  made 
of  this  material  should  not  be  heated  above  a  bright  cherry- 
red  nor  should  they  be  heated  in  a  thin  fire,  especially  in  one 
having  a  forced  blast,  such  as  an  ordinary  blacksmith's  fire.  In 


BOILER  CALCULATIONS 


53 


such  a  fire  ther^  will  be  an  excess  of  air  which  will  attack  the 
steel  and  cause  it  to  burn. 

The  button  head  is  the  style  generally  made  when  the  riveting 
is  done  by  machinery.  With  hand  riveting  it  is  more  common 
to  make  what  is  called  a  steeple  head,  having  the  shape  of  a  full 
cone  as  shown  in  Figs.  32  and  33. 

The  height  of  the  steeple  head  should  be  about  three-fourths 
or  seven-eighths  the  diameter  of  the  rivet,  and  the  greatest 
diameter  about  two  times  the  diameter  of  the  rivet.  The  height 


FIG.  34. — Forces  acting  upon  riveted  joints. 

of  the  button  or  round  head  should  be  five-eighths  or  three- 
fourths  the  diameter  of  the  rivet  while  the  greatest  diameter  of 
the  head  should  be  one  and  three-fourths  times  the  diameter  of  the 
rivet.  For  either  type  of  head  the  allowance  of  extra  length  of 
shank  for  forming  the  head  is  2|  times  the  diameter  of  the  shank 
for  hand  riveting;  but  for  machine  riveting,  the  allowance  is 
from  1/16  to  1/8  in.  greater.  In  addition  to  the  above,  there 
should  be  an  allowance  of  1/16  in.  for  each  plate  when  more 
than  two  plates  are  to  be  joined  together. 

Rivets  which  are  too  long  should  not  be  used,  as  the  cup  die 
will  form  a  ring  around  the  head  and  this  will  have  to  be  trimmed 
in  order  to  present  a  good  appearance.  Neither  should  the_rivet 


54  STEAM  BOILERS 

be  too  short,  as  the  plate  around  the  circumference  of  the  head 
will  be  more  or  less  nicked  by  the  edge  of  the  cup  die,  if  the 
riveting  is  done  by  machine. 

To  test  the  tightness  of  the  rivet,  the  thumb  should  be  placed 
on  the  head  and  the  forefinger  on  the  plate.  By  striking  the 
head  with  the  hammer,  any  looseness  of  the  rivet  may  be  felt. 

When  steam  is  raised  in  a  boiler,  the  pressure  exerts  a  pull  or 
tension  in  the  metal  of  the  shell.  With  a  lap  joint  such  as  shown 
at  a  of  Fig.  34  or  a  butt  joint  with  a  single  cover  plate  such  as 
shown  at  c,  this  tension  will  tend  to  pull  the  joints  into  the 
shapes  shown  at  b  and  d  of  Fig.  34. 

The  bending  action  comes  into  play  every  time  a  boiler  is  fired 
up,  the  plates  again  straightening  out  when  the  boiler  cools. 
This  continual  bending  action  in  lapped  joints  and  in  single 
strapped  butt  joints  often  causes  cracks  to  be  formed  in  the 
plates  beneath  the  laps.  These  cracks  are  widened  by  corrosion 
and,  as  they  are  hidden,  are  very  dangerous.  For  this  reason, 
if  single  straps  are  used,  the  straps  should  always  be  placed  on 
the  outside  of  the  shell.  Then,  if  cracks  appear,  they  will  be 
on  the  outside  where  they  will  not  be  acted  upon  by  the  water 
and  where  they  may  be  detected. 


CHAPTER   IV 
STAYS  AND  STAYING 

36.  Principles  of  Staying. — The  pressure  within  a  boiler  tends 
to  force   the    shell   into  a  true  cylindrical    shape,  if  it   is  not 
already  so.     Likewise  it  tends  to  force  the  heads  into  a  true 
hemispherical    shape.     This    means    that    all    surfaces    under 
pressure,  which  do  not  have  one  of  these  forms,  must  be  braced 
to  prevent  this  change  of  ^shape. 

Stays  should  fulfill  three  conditions.  First,  if  the  plate  is  flat 
or  nearly  so,  they  should  be  sufficient,  both  in  number  and  size, 
to  support  the  plate  entirely,  without  regard  to  its  stiffness. 
Second,  they  should  be  spaced  so  as  to  allow  a  free  inspection 
of  the  boiler.  Third,  they  should  not  interfere  with  the  circu- 
lation of  water. 

A  stay  should  pull  at  right  angles  to  the  surface  which  it 
supports,  and  should  be  fastened  squarely  to  the  plate  instead 
of  at  an  angle  to  it. 

Stays  should  be  fitted  in  their  places  tight  enough  to  prevent 
shaking  and  should  all  pull  equally.  On  the  other  hand,  a  stay 
should  not  be  strained  into  place,  as  this  is  apt  to  overload  it. 
All  stays  should  be  carefully  fitted  into  place,  as  they  are  out  of 
sight  for  considerable  periods  -of  time  and  there  is  no  way  of 
determining  their  efficiency  except  by  the  failure  of  the  boiler. 

37.  Stay  Bolts. — The  simplest  form  of  stay  is  used  when  two  flat 
surfaces  are  near  each  other,  as  the  sides  of  the  water  legs  of 
a  locomotive  boiler  which  are  stayed  by  means  of  stay  bolts. 
These  bolts  are  about  6  in.  long  and  are  threaded  at  both  ends. 
The  bolts  are  screwed  into  both  plates  and,  if  the  plates  have  a 
thickness  greater  than  half  the  diameter  of  the  bolt,  the  ends 
are  riveted  over,  as  in  Fig.  35.     If  the  plates  have  a  thickness 
less  than  half  the  diameter  of  the  bolt,  they  are  usually  held  by 
nuts  and  washers,  as  in  Fig.  36.     The  heads  of  the  stay  bolts  are 
upset  so  that  they  will  be  the  same  size  at  the  root  of  the  thread 
as  the  balance  of  the  bolt.     They  are  also  made  by  threading  the 
bolt  throughout  its  length  and  then  turning  off  the  thread  in 

6  55 


56 


STEAM  BOILERS 


the  middle  portion  of  the  bolt.  This  is  an  excellent  method  as 
it  gives  a  continuous  thread  and  yet  leaves  the  body  of  the 
bolt  smooth,  making  it  less  liable  to  corrosion  than  if  the  threads 
are  left  on  it.  Sometimes  a  small  hole  (see  Fig.  35)  is  bored  in 
the  center  of  the  bolt,  extending  a  little  beyond  the  thread. 
When  these  bolts  break,  they  usually  do  so  near  the  plate  which 
they  are  holding  and,  in  case  of  a  break,  steam  or  water  will 
flow  through  the  hole  in  the  bolt,  giving  warning  of  the  break. 
Such  bolts  are  called  safety  stay  bolts. 

The  stay  bolts  described  above  are  objectionable  because 
of  their  stiffness.  There  is  a  considerable  difference  of  tem- 
perature between  the  inner  and  outer  sheets  of  the  water  leg  of  a 
locomotive  type  of  boiler,  where  stay  bolts  are  most  used,  and, 


FIG.  35. 


FIG.  36. 


due  to  the  greater  expansion  of  one  sheet  over  another,  the 
rigid  stay  bolts  are  liable  to  break.  To  prevent  the  constant 
breaking  of  these  bolts,  many  types  of  flexible  stay  bolts  have 
been  designed.  One  of  the  common  types  of  these  is  shown  in 
Fig.  37.  This  consists  of  a  steel  bolt  threaded  at  one  end  and 
having  a  spherical  head  at  the  other.  The  spherical  head 
rests  in  a  cup-shaped  collar  which  screws  into  the  outer  plate  of 
the  water  leg.  This  collar  is  first  screwed  into  the  outer  plate, 
after  which  the  bolt  is  run  through  and  screwed  into  the  inner 
plate  until  the  spherical  head  has  a  firm  bearing  against  the 
collar.  The  bolt  head  is  slotted  to  receive  a  large  screw  driver 
which  is  used  in  screwing  it  into  the  inner  plate.  The  threaded 
end  of  the  bolt  may  be  riveted  over  after  being  screwed  through 
the  inner  plate,  or  it  may  be  fitted  with  a-  nut  and  washer  to 
prevent  the  bolt  working  loose.  A  cap  is  screwed  on  the  collar 


STAYS  AND  STAYING 


57 


to  cover  the  end  of  the  bolt,  giving  it  a  neater  appearance, 
preventing  dirt  from  collecting  between  the  bearing  surfaces, 
and  preventing  the  escape  of  any  steam  or  water  that  may  leak 
past  the  head  of  the  bolt.  This  form  of  stay  bolt  allows  consid- 
erable movement  between  the  plates  and  at  the  same  time  main- 


FIG.  37.— Flexible  stay  bolt. 

tains  a  tight  joint.  It  has  the  objection,  however,  that  there 
may  not  always  be  enough  space  for  the  large  cap  in  the 
location  in  which  the  bolt  is  most  used.  In  addition  to  this,  it 
is  very  difficult  to  remove  a  broken  bolt  unless  it  is  fitted  with 
a  nut  and  washer  on  the  threaded  end,  and  these  are  objection- 
able in  a  fire  box  because  they  are  liable  to  be  burned. 


FIG.  38.— Flexible  stay  bolt. 

To  overcome  the  objection  that  the  flexible  stay  bolt  de- 
scribed above  occupies  too  much  space,  the  design  shown  in  Fig. 
38  has  been  made  for  use  in  those  locations  in  which  there  is 
not  enough  space  to  accommodate  the  other  type.  In  this 
design  the  bearing  between  the  collar  and  bolt  is  in  the  bottom 
of  the  collar  instead  of  near  the  top,  and  instead  of  an  outer 


58 


STEAM  BOILERS 


cap  being  used,  a  flat  cap  is  screwed  into  the  end  of  the  collar. 
This  type  of  stay  bolt  may  be  placed  flush  with  the  outer  plate 
and  thus  occupy  even  less  space  than  the  ordinary  form  of 
rigid  stay  bolt. 

A  type  of  flexible  stay  bolt  which  is  easier  to  remove  than 
either  of  those  described  above  is  shown  in  Fig.  39.  This  bolt 
is  threaded  at  both  ends  and  the  spherical  head  is  in  the  form 
of  a  nut  which  screws  on  the  bolt.  This  form  of  bolt  has  the 
further  advantage  that  it  may  be  readily  tightened  if  it  should 
become  loose. 


FIG.  39. — Flexible  stav  bolt. 


38.  Boiler  Heads. — The  pressure  of  the  steam  on  a  boiler  head 
acts  at  right  angles  to  the  inner  surface  of  the  head.  The  heads 
of  fire-tube  boilers  are  necessarily  flat,  and  flat  plates  begin 
to  bulge  out  at  very  low  pressures  unless  they  are  braced,  as 
there  is  nothing  to  resist  the  bulging  except  the  stiffness  of  the 
plate,  which  offers  very  little  resistance.  It  is  common  practice 
in  boiler  construction  to  transfer  these  strains  from  the  flat  head 
to  some  part  of  the  boiler  shell.  As  this  transference  brings 
additional  strains  upon  the  shell,  the  fastenings  for  the  stays 
must  not  be  brought  too  near  together,  since  the  shell  may  then 
be  weakened.  Boiler  heads  may  be  braced  either  by  diagonal 
stays  extending  from  the  head  to  the  side  of  the  boiler  shell,  or 
by  means  of  long  rods  extending  entirely  through  the  boiler  from 
one  head  to  the  other,  the  rods  being  threaded  at  the  ends  and 
screwed  into  the  heads,  or  fitted  with  a  washer  and  nut.  Such 
a  rod  or,  as  it  is  more  commonly  called,  a  through  stay  is  illus- 
trated in  Fig.  36. 

The  holding  power  of  tubes  expanded  into  the  tube  sheets  is 


STAYS  AND  STAYING  59 

sufficient  to  brace  this  portion  of  the  head  against  any  ordinary 
pressure,  unless  the  boiler  is  unusually  large,  as  in  the  Scotch 
marine  type.  It  is  then  sometimes  desirable  to  use  a  few  extra 
heavy  tubes  which  are  threaded  and  screwed  into  the  heads  to 
act  as  both  tubes  and  braces. 

Boiler  heads  are  usually  flanged  and  riveted  to  the  shell.  In 
case  this  is  done,  the  flanging  gives  additional  stiffness  to  the  head 
so  that  no  bracing  need  be  applied  nearer  than  3  in.  to  the  point 
where  the  curvature  of  the  flange  begins.  In  the  same  manner, 
the  top  row  of  tubes  offers  sufficient  staying  for  a  distance  of  2 
in.  above  this  row  of  tubes.  This  leaves  the  unsupported  area 


oooooooooo 


FIG.  40. 

as  shown  in  Fig.  40,  and  the  stays  or  braces  should  be  sufficient 
to  support  the  pressure  on  this  area,  and  they  should  be  of  uni- 
form size  and  spacing  so  that  all  parts  of  this  area  will  be  sup- 
ported equally. 

39.  Diagonal  Stays. — Sometimes  it  is  desirable  to  have  the 
central  part  of  the  shell  free  from  stays  and,  if  such  is  the  case, 
diagonal  stays  may  be  used  to  advantage  to  stay  the  heads  of 
boilers.  Diagonal  stays  are  fastened  to  the  head  of  the  boiler 
and  to  the  shell,  as  in  Fig.  41.  A  stay  exerts  a  pull  on  the  head 
in  the  direction  abj  Fig.  41,  but  only  the  horizontal  component 
or  projection  of  this,  as  represented  by  the  line  ac,  is  effective 
for  resisting  the  pressure  to  be  supported  by  the  stay.  Fig.  42 
shows  four  of  the  most  common  types  of  diagonal  stays.  The 
lower  ends  in  the  figure  show  the  methods  of  attaching  to  the 
head.  The  other  ends  are  riveted  solidly  to  the  shell.  An 
illustration  of  the  application  of  diagonal  stays  is  shown  in  Fig.  7 


60 


STEAM  BOILERS 


where  the  heads  of  the  return  fire-tube  portable  boiler  shown 
there  are  braced  by  this  means. 

40.  Girder  Stays. — These  are  used  for  supporting  the  crown- 
sheet  or  top  of  the  combustion  chamber  in  locomotive  and  in 


FIG.  41. — Forces  in  diagonal  stay. 

Scotch  marine  boilers.  This  form  of  stay  acts  as  a  beam  or 
girder  resting  on  the  side  sheets  of  the  combustion  chamber 
and  supporting  the  crown-sheet  by  means  of  bolts  passing  through 
it  and  through  the  girder  stay  as  shown  in  Figs.  43  and  44.  An 


FIG.  42. — Types  of  diagonal  stays. 


open  space  is  left  between  the  crown-sheet  and  the  girder  to 
permit  free  circulation  of  the  water. 

The  girder  should  be  chipped  and  filed  until  it  sets  perfectly, 
resting  not  only  on  the  edge  of  the  side  sheets,  but  also  on  the 
curved  edge  of  the  crown-sheet.  Two  forms  of  girders  are 
illustrated  here:  The  one  shown  in  Fig.  44  consisting  of  two 


STAYS  AND  STAYING 


61 


parallel  girders  formed  from  steel  plates,  which  is  the  older  and 
more  common  form;  and  the  other,  shown  in  Fig.  43,  consisting 
of  a  single  forged  or  cast  girder,  with  holes  for  the  bolts  bored 
through  enlarged  portions  of  it.  The  bolts  used  to  support  the 
crown-sheet  are  plain  round  bolts  threaded  at  one  end  only,  and 


FIG.  43. — One-piece  girder  stay. 


FIG.  44. — Two-piece  girder  stay. 

with  round  heads.  The  bolts  pass  up  through  the  crown-sheet 
and  girder  and  are  fastened  on  top  by  a  nut  which  bears  against 
a  washer  resting  on  top  of  the  girder.  Thimbles  or  distance 
pieces  are  placed  between  the  girder  and  crown-sheet,  and  the 
nuts  are  screwed  up  till  the  crown-sheet  rests  against  them. 


62  STEAM  BOILERS 

This  stiffens  the  crown-sheet  and  forms  a  steam-  and  water- 
tight joint. 

In  locomotive  boilers,  the  girder  stay  is  sometimes  so  long  that 
it  must  be  supported  differently.  This  is  done  by  having  short 
stays,  called  sling  stays,  fastened  to  the  girder  and  to  the  top 
sheet  of  the  boiler.  If  this  were  not  done,  the  girder  would  have 
to  be  so  large,  in  order  for  it  to  have  sufficient  stiffness,  that  it 
would  interfere  seriously  with  the  circulation.  In  this  way,  the 
girder  is  supported  by  the  top  sheet,  and  the  crown-sheet  is 


FIG.  45. — Sling  stay. 

supported  by  the  girder.  This  is  equivalent  to*  having  through 
stays  from  the  crown-sheet  to  the  top  sheet  of  the  boiler,  except 
that  this  arrangement  is  more  flexible.  A  crown-sheet  sup- 
ported by  a  girder  and  sling  stays  is  illustrated  in  Fig.  45.  The 
use  of  a  girder  stay  to  support  the  top  of  the  combustion  chamber 
of  a  Scotch  marine  boiler  is  illustrated  in  Fig.  14. 

Girder  stays  are  not  used  as  extensively  now  for  supporting  the 
crown-sheet  of  locomotive  boilers  as  they  were  a  few  years  ago. 
This  method  of  support  is  being  replaced  by  the  use  of  radial 
stays.  These  are  in  the  form  of  bolts  threaded  at  both  ends  like 
a  stay  bolt,  and  screwed  into  both  crown-sheet  and  shell  of  the 
boiler  and  then  riveted  over.  By  using  the  proper  number  and 
size  of  radial  stays,  the  crown-sheet  is  supported  equally  at  all 
points,  and  as  they  are  placed  in  regular  rows  they  do  not  interfere 
seriously  with  the  circulation.  The  use  of  radial  stays  in  sup- 
porting the  crown-sheet  of  a  locomotive  boiler  is  shown  in  Figs. 
9  and  10. 


STAYS  AND  STAYING 


63 


41.  Gusset  Stays. — Gusset  stays  are  a  form  of  diagonal  stay, 
but  are  made  from  plates  and  are  attached  to  angles  which  are 
riveted- to  the  head  and  to  the  sides  of  the  boiler,  as  shown  in 
Fig.  46.  They  are  quite  commonly  used  in  Cornish  and  Lan- 
cashire boilers,  but  have  the  faults  that  they  are  exceedingly 


rigid,   take   up   considerable 
stresses  in  them  is  difficult. 


space,  and  the   determination   of 


FIG.  46.— Gusset  stay. 

42.  Stay  Tubes. — Boiler  tubes  also  act  as  stays  if  the  ends  are 
properly  beaded  over  and,  where  they  are  used,  no  other  stays 
are  needed  to  hold  the  tube  sheets.     The  surface  of  the  head 
above  the  tubes  must,  however,  be  stayed.     In  marine  boilers, 
some  of  the  tubes  are  made  extra  heavy  and  have  the  ends  upset 
and  screwed  into  the  heads  for  the  purpose  of  giving  extra 
support.     These  are  called  stay  tubes. 

43.  Radial  Stays. — These  are  used  between  two  surfaces  which 
have  different  radii  of  curvature,  such  as  the  crown-sheet  and 


FIG.  47. 


FIG.  48. 


FIG.  49. 


top  of  a  locomotive  fire  box.  Fig.  47  shows  a  common  form  of 
radial  stay.  One  of  the  threaded  ends  is  upset  to  a  size  1/8  in. 
larger  than  the  other  in  order  to  allow  the  small  end  to  be  passed 
through  without  screwing.  The  ends  of  the  stay  are  riveted 


64  STEAM  BOILERS 

over  after  it  is  screwed  into  place.  Fig.  48  is  another  type  of 
bolt  for  the  same  purpose.  This  requires  a  copper  washer, 
which  should  be  not  less  than  1/8  in.  thick,  under  the  nut. 
Where  this  bolt  is  used  at  an  angle  to  the  plates,  the  head  and 
nut  must  be  faced  off  to  a  wedge  shape,  and  the  copper  washers 
made  to  fit,  as  in  Fig.  49. 

44.  Through  Stays. — Such  stays  are  made  of  round  rods,  as  in 
Fig.  36,  threaded  at  both  ends  and  supplied  with  washers  and 
nuts  on  each  side  of  the  plate  to  stiffen  it.    The  ends  of  the  stays 
are  upset  in  order  to  make  the  threaded  portion  as  strong  as  other 
parts  of  the  rod.     Through  stays  are  used  to  connect  together 
the  two  heads  of  a  boiler  and  are  used  chiefly  on  marine  boilers. 
Fig.  14  illustrates  their  use  for  the  latter  purpose. 

45.  Dished  Heads. — The  internal  pressure  of  a  boiler  acting  on 
a  flat  head  tends  to  bulge  it  out  into  a  spherical  shape.     There- 
fore if  a  boiler  head  is  made  of  a  spherical  shape  it  will  require 
no  bracing,  as  it  is  already  in  the  shape  which  the  pressure  tends 
to  make  it.     It  is  impossible  to  make  the  heads  of    fire-tube 
boilers  in  this  shape  as  the  tubes  must  be  placed  in  them  at  right 
angles  to  the  head  in  order  to  bead  them  over  properly,  but 
when  steam  drums  are  used  on  water-tube  boilers,  the  heads  of 
these  are  practically  always  made  of  a  spherical  shape.     Heads 
shaped  to  this  form  are  called  "cambered,"  dished,"  or  "bumped" 
heads.     If  they  are  dished  to  twice  the  radius  of  the  shell,  the 
head  and  shell  will  be  equally  strong  to  resist  bursting. 

When  heads  are  made  they  are  usually  flanged  to  fit  inside  the 
shell  and  are  then  riveted,  a  single  riveted  joint  being  used. 

46.  Tube  Setting. — When  for  any  reason  it  becomes  necessary 
to  renew  a  tube  in  a  boiler,  the  old  tube  must  be  carefully  removed . 
The  old  tube  may  be  quickly  removed  by  first  crushing  the  ends 
of  the  tube  with  a  cold  chisel  and  hammer  to  release  the  beading 
from  the  tube  plate.     During  this  process  great  care  should  be 
exercised  to  prevent  injury  to  the  hole  in  the  plate.     If  it  is  desired 
to  preserve  the  tube  this  method  is  objectionable  because  the 
tube  is  very  liable  to  be  split  and  ruined. 

If  it  is  desired  to  preserve  the  tube,  either  of  two  methods  may 
be  employed.  First,  a  tube  cutter  may  be  used  to  cut  the  tube 
where  it  is  expanded  in  the  heads  and  at  a  point  about  two- 
thirds  through  the  thickness  of  the  head.  This  leaves-  both  the 
tube  and  a  short  nipple  remaining  in  the  head.  The  nipple  may 
now  be  crushed  with  a  cold  chisel  and  removed.  In  order  to 


STAYS  AND  STAYING  65 

remove  the  tube  it  will  be  necessary  to  make  its  ends  smaller 
by  passing  an  oyster  chisel  around  it  between  the  tube  and  the 
head,  when  the  tube  may  be  easily  slipped  out.  This  method 
cannot  be  used  if  there  is  a  bead  on  the  tube  just  inside  the  head, 
like  that  shown  in  Fig.  53,  which  is  left  by  some  kinds  of  tube 
expanders.  The  second  method  mentioned  above  may  be 
employed  in  this  case.  By  this  method,  the  tube  is  cut  inside 
the  head  by  means  of  a  tube  cutter.  The  nipple  remaining  in 
the  head  is  crushed  and  removed  and  the  tube  slipped  out. 

As  there  is  always  more  or  less  irregularity  in  every  tube  plate 
it  will  be  necessary  to  measure  each  tube  separately.  This  can 
best  be  done  by  means  of  a  small  gas  pipe  of  sufficient  length,  as 
it  is  quite  stiff  for  its  weight  and,  being  small,  it  is  easily  caught 
at  the  farther  end.  The  measuring  pipe  should  be  held  flush 
with  the  far  end  by  a  helper  while  being  marked  close  against  the 
plate  at  the  near  end.  A  block  of  wood  held  over  the  hole  at  the 
far  end  by  the  helper  will  assist  in  keeping  the  measuring  pipe 
flush  with  the  tube  plate.  A  slate  pencil  is  useful  in  marking 
the  measuring  pipe  and  avoids  the  confusion  which  is  likely  to 
result  from  scratches  on  the  pipe  which  cannot  be  removed. 

When  the  distance  between  the  tube  plates  has  been  obtained 
in  the  way  described  above,  the  measuring  pipe  may  be  removed 
and  laid  alongside  the  tube,  and  this  marked  to  the  proper  length. 
Enough  extra  length  of  tubing  should  be  measured  off  to  allow 
for  beading.  A  length  at  each  end  of  from  two  to  two  and 
one-half  times  the  thickness  of  the  walls  of  the  tube  is  sufficient 
to  allow  for  beading. 

If  copper  ferrules  are  to  be  used  on  the  ends  of  the  tubes,  the 
tubes  have  to  be  swaged  to  admit  the  ferrule.  If  this  is  not  done 
it  will  be  necessary  to  enlarge  the  hole  in  the  tube  sheet,  and 
usually  the  holes  are  so  close  together  as  not  to  permit  of  this. 
The  ferrules  should  not  project  beyond  the  tube  sheet  more 
than  enough  to  give  them  a  hold  and  allow  the  tubes  to  be 
beaded  over. 

In  placing  the  tubes,  they  are  run  through  the  front  sheet, 
while  the  helper  catches  them  with  a  short  rod  at  the  far  end, 
directing  this  end  into  place.  The  excess  length  of  tube  should 
now  be  divided  so  that  an  equal  amount  projects  beyond  each  tube 
sheet.  While  setting  one  end  of  the  tube  the  other  end  should 
be  held  to  its  proper  position  by  the  helper.  For  this  purpose 


66  STEAM  BOILERS 

a  block  of  iron  with  a  recess  in  it,  such  as  shown  in  Fig.  50,  will 
be  found  convenient. 

If  the  tube  has  been  cut  off  by  a  cutter  which  works  on  the 
inside  of  the  tube,  it  is  now  ready  for  expanding  in  the  head. 
Cutting  off  the  tube  in  this  way  leaves  a  bevelled  edge,  the  bead 
being  turned  outward,  which  makes  it  easy  to  bead. 

A  thin  steel  tube  can  be  expanded  in  a  bored  hole  so  as  to 
make  a  steam-  and  water-tight  joint  by  means  of  a  tool  called 
a  tube  expander.  It  is  not  practical  to  expand  tubes  having  a 
greater  diameter  than  5  in.  Tubes  larger  than  this  are  commonly 
riveted  to  flanged  holes  in  the  tube  sheet. 


FIG.  50. 


There  are  two  types  of  tube  expanders  in  common  use,  known 
as  the  Prosser  expander,  illustrated  in  Fig.  51,  and  the  Dudgeon 
expander,  shown  in  Fig.  52.  The  Prosser  expander  consists  of 
a  number  of  steel  segments  held  together  by  a  spring  steel  band, 
or  by  a  rubber  ring,  the  segments  being  of  such  size  that  when 
the  expander  is  collapsed  it  is  of  smaller  size  than  the  tube, 
and  may  be  inserted  into  it.  A  tapered  steel  pin  passes  through 
the  center  of  these  steel  segments  and,  by  driving  this  tapered 
pin  in,  the  segments  are  separated  and  bear  against  the  tube. 
By  gradually  driving  in  the  pin,  then  slacking  and  turning  it 
and  driving  again,  the  tube  is  expanded  until  it  completely  fills 
the  hole  in  the  tube  sheet.  Tubes  which  are  put  in  by  this 
method  are  expanded  on  both  sides  of  the  tube  sheet  and  act  as 
braces  to  stiffen  it. 

The  Dudgeon  expander  is  designed  to  expand  the  tube  by  the 
continuous  pressure  of  steel  rollers  turning  inside  the  tube.  It 


STAYS  AND  STAYING  67 

consists  of  a  hollow  cylinder  provided  with  openings  to  receive 
three  or  more  steel  rollers.  A  tapered  steel  mandrel  is  placed  in 
a  hole  in  the  center  of  the  cylinder  and  bears  against  the  steel 
rollers.  By  revolving  the  expander  and  at  the  same  time 
hitting  the  mandrel  with  a  wooden  mallet  the  rollers  are  gradu- 
ally forced  outward  and  this  expands  the  tube.  If  the  expander 
is  run  by  power,  the  motor  will  stall  when  the  tube  has  been 


FIG.  51. — Prosser  tube  expander. 

expanded  and  there  will  be  no  danger  of  rolling  it  too  thin.  If 
the  expander  is  run  by  hand,  it  will  pull  so  tightly  when  the 
tube  has  been  expanded  that  the  workman  will  stop  of  his  own 
accord. 

By  placing  the  steel  rolls  of  a  Dudgeon  expander  at  an  angle, 
as  shown  in  Fig.  52,  the  expander  is  made  self-feeding  and  it  is 
not  necessary  for  the  workman  to  drive  the  mandrel.  When 


FIG.  52. — Dudgeon  tube  expander. 

the  tube  has  been  expanded  sufficiently,  it  is  only  necessary  to 
turn  it  backward  to  loosen  it.  These  expanders  are  made  to  be 
operated  by  either  hand  or  power  and  they  are  provided  with 
extra  long  rolls  which  may  be  reversed  after  one  end  has  become 
worn,  thus  greatly  lengthening  the  life  of  the  expander. 

After  the  tube  has  been  expanded  by  either  of  the  methods 
described  above,  the  ends  of  the  tube  that  project  beyond  the 
tube  sheet  should  be  neatly  beaded  over  by  means  of  a  beading 
tool  called  a  "boot,"  which  is  illustrated  in  Fig.  53.  The  tool 


68 


STEAM  BOILERS 


should  be  held  greatly  inclined  to  the  tube  at  first,  as  shown  by 
the  dotted  lines,  until  the  end  of  the  tube  is  well  flared  out. 
After  this  is  done,  the  tool  may  be  held  nearly  parallel  with  the 
flue,  as  illustrated,  and  the  beading  finished  neatly. 


FIG.  53. — Boot. 


47.  Manholes  and  Handholes. — Any  boiler  which  has  a  steam 
or  water  space  large  enough  to  admit  a  man  should  be  pro- 
vided with  a  manhole.  There  is  no  standard  size  for  man- 
holes but  most  of  them  are  11  in.  X15  in.,  which  is  large  enough 
to  admit  a  good-sized  man.  The  best  location  for  a  manhole  is 
in  the  end  of  a  boiler  above  the  tubes  for  fire-tube  boilers  or  in 
the  end  of  the  steam  drum  of  a  water-tube  boiler.  It  is  often 
impractical  to  place  the  manhole  in  the  end  of  a  fire-tube  boiler, 
as  the  head  is  flat  and  requires  stays  which  may  have  to  come 
at  the  point  which  the  manhole  would  occupy.  In  this  case 
they  have  to  be  placed  in  the  top  of  the  shell,  but  the  latter 
location  is  not  so  good  unless  the  boiler  is  large,  because  of  the 
difficulty  a  man  has  in  straightening  himself  out  in  the  small 
height  between  the  top  of  the  tubes  and  the  top  of  the  shell. 

Unless  the  manhole  is  flanged,  it  should  be  strengthened  by 
a  ring  of  steel  or  wrought  iron  riveted  to  the  inside  of  the  shell. 
This  will  restore  the  strength  lost  by  cutting  so  much  metal  out 
of  the  sheet.  There  is  a  disadvantage,  however,  in  the  use  of 
such  a  strengthening  ring  in  that  the  rivets  come  where  the 
manhole  cover  rests,  and  for  this  reason  only  countersunk 
rivets  can  be  used. 


STAYS  AND  STAYING 


69 


A  later  and  better  practice  is  to  flange  the  manhole,  the 
flanges  being  on  the  inside.  This  flange  gives  the  additional 
strength  needed  and,  by  facing  off  the  flange,  it  forms  a  good 
seat  for  the  cover.  The  cover  is  usually  stamped  out  of  steel 


FIG.  54. — Lukens  manhole  and  cover. 


FIG.  55. — Handhole  for  water-tube  boiler. 

and  goes  inside  the  boiler,  being  kept  firmly  to  its  seat  by  a  bolt 
which  passes  through  the  cover  and  through  a  steel  yoke 
which  bridges  across  the  manhole  on  the  outside.  A  manhole 
and  cover  constructed  in  this  manner  is  illustrated  in  Fig.  54, 
which  shows  a  Lukens  manhole  and  cover.  A  gasket  which  is 


70  STEAM  BOILERS 

not  affected  by  either  heat  or  water  should  be  placed  between 
the  manhole  cover  and  its  seat. 

Handholes  are  shaped  like  manholes  but  are  smaller  in  size. 
They  are  used  in  front  of  the  tubes  of  water-tube  boilers  and 
below  the  tubes  in  small  fire-tube  boilers.  In  the  larger  sizes 
of  fire-tube  boilers  a  manhole  is  placed  below  the  tubes  instead 
of  a  handhole.  Fig.  55  shows  a  handhole  such  as  is  usually  placed 
in  front  of  a  tube  in  a  water-tube  boiler.  The  cover  is  fitted 
with  a  gasket  to  make  a  steam-  and  water-tight  joint  and  the 
cover  is  of  such  shape  as  to  prevent  the  gasket  from  being  blown 
out.  The  cover  is  held  by  a  single  bolt  screwed  through  the  cover 
and  then  riveted  over.  The  bolt  then  passes  through  a  steel 
yoke  and  is  held  in  place  by  a  nut  on  the  outside. 


CHAPTER  V 
HEAT  AND  WORK 

48.  Changing  Heat  into  Work. — Since  a  boiler  is  a  device 
for  making  steam  from  water  by  the  application  of  heat  it  is 
essential  that  we  have  a  thorough  understanding  of  the  nature 
of  heat,  how  it  acts  and  how  steam  is  formed.  We  must  keep 
in  mind  always  that  it  is  the  heat  which  does  the  work  and  not 
the  steam.  From  this  property  of  heat  by  which  it  is  able  to  do 
work  we  say  that  heat  is  a  form  of  energy,  for  energy  is  the 
ability  to  do  work. 

In  a  steam  power  plant  we  start  with  a  coal  fire  on  the  grate 
and  with  water  in  the  boiler  and  finally  get  mechanical  energy  or 
electric  current  to  be  sent  out  from  the  plant.  The  coal  is  burned, 
and  the  heat  thus  liberated  is  used  to  evaporate  water  and 
supply  steam  under  pressure.  The  steam  goes  to  the  engine, 
where  part  of  its  heat  is  transformed  into  mechanical  energy. 
We  see,  then,  that  the  fuel  is  the  starting-point  and  is  the  real 
source  of  energy.  We  will  now  study  the  process  by  which 
the  energy  of  the  fuel  is  utilized  in  a  power  plant. 

Consider  the  elementary  power  plant  illustrated  in  Fig.  56 
which  shows  all  the  apparatus  needed  to  convert  heat  energy 
into  mechanical  work.  The  coal  is  fed  into  the  furnace,  where 
a  small  part  of  it  is  lost  by  dropping  through  the  grate  in  the 
form  of  small  particles  of  unburned  coal.  The  larger  part  of 
the  coal  is  burned  and,  of  the  total  heat  generated  thereby,  one 
part  is  lost  out  of  the  stack  and  another  part  passes  into  the 
water  in  the  boiler  to  form  steam. 

Of  the  heat  which  enters  the  boiler  a  very  small  portion  is  lost 
through  radiation  from  the  exposed  portions  of  the  boiler,  but 
by  far  the  larger  portion  enters  the  water,  raises  its  temperature 
and  causes  the  water  to  boil  and  form  steam.  The  steam  thus 
formed  passes  out  of  the  boiler  through  the  steam  pipe,  part  going 
to  the  engine  cylinder  and  part  going  to  the  pumps.  A  small 
amount  of  heat  will  be  lost  by  radiation  from  the  hot  steam 
pipes  and  from  the  hot  cylinder  of  the  engine  and  pump.  The 
7  71 


72 


STEAM  BOILERS 


4%-  540  at  U. 


•••Illlll 


FIG.  56. — What  becomes  of  the  heat  in  the  fuel. 


HEAT  AND  WORK  73 

remaining  portion  which  enters  the  engine  cylinder  causes  the 
piston  to  move,  at  the  same  time  losing  its  pressure.  The  motion 
of  the  piston  is  transferred  to  the  flywheel  where  the  energy  may 
be  taken  off  by  belts. 

Only  a  small  part  of  the  heat  energy  delivered  to  the  cylinder 
reaches  the  flywheel.  A  small  part  of  it  is  lost  in  friction  in  the 
moving  parts  of  the  engine  and  a  far  greater  part  is  exhausted 
from  the  cylinder  in  the  form  of  exhaust  steam.  Upon  leaving 
the  cylinder,  the  exhaust  steam  passes  to  a  condenser,  where 
it  is  changed  back  into  water  and  in  doing  so  gives  up  its  heat 
to  the  water  which  condenses  it,  and  thereby  raises  the  tem- 
perature of  the  condensing  water.  A  portion  of  this  water  is 
fed  into  the  boiler  to  take  the  place  of  the  steam  used  in  running 
the  engine  and  pumps.  The  remaining  hot  water  is  wasted. 

A  small  amount  of  steam  is  used  in  the  boiler-feed  pump, 
where  it  does  work  in  pumping  water  into  the  boiler,  but,  as 
in  the  case  of  the  engine,  the  larger  part  of  the  steam  taken 
by  the  pump  is  lost  in  the  exhaust.  We  see  from  the  above 
description  that  the  water  used  in  a  boiler  passes  through  a 
regular  cycle  of  events  whereby  it  takes  up  heat  and  carries 
it  to  the  engine,  where  a  portion  of  the  heat  is  turned  into  work 
and  another  portion  is  wasted,  the  water  returning  to  the  boiler 
in  the  form  of  water  and  leaving  it  in  the  form  of  steam. 

49.  Work. — The  prime  object  of  any  power  plant  is  to  do  work. 
By  work  we  mean  the  overcoming  of  resistance  and  the  pro- 
ducing of  motion.  When  the  steam  in  an  engine  cylinder  exerts 
a  sufficient  force  to  overcome  the  resistance  of  the  load  and  to 
cause  the  piston  to  move,  work  is  done.  There  are  two  parts 
or  factors  to  work;  the  force  used  and  the  distance  moved.  The 
same  force  will  do  more  work  in  moving  a  body  a  long  distance 
than  in  moving  it  a  short  distance.  Also,  for  the  same  distance,  a 
large  force  will  do  more  work  than  a  small  one.  Work  is,  there- 
fore the  product  of  the  moving  force  and  the  distance,  and  is 
generally  expressed  in  foot-pounds. 

One  Foot-pound  is  the  work  done  when  a  force  of  1  Ib.  is  exerted 
for  a  distance  of  1  ft.  If  a  weight  of  80  Ib.  is  lifted  1  ft.,  the  force 
required  will  be  80  Ib.,  because  we  measure  a  force  by  the  weight 
it  can  lift.  If  this  force  lifts  the  weight  through  a  distance  of 
4  ft.  the  work  done  will  be  4X80  =  320  foot-pounds.  It  will 
require  the  same  amount  of  work  toJift^O  Ib.  8  ft.  or^lG  Ib.  20  ft. 
If  the  piston  of  an_engine  travels  750  ft.  in  a  minute  and  the 


74  STEAM  BOILERS 

average  pressure  on  the  piston  during  this  time  is  10,000  lb., 
the  work  done  during  one  minute  will  be  750  X  10,000  =  7,500,000 
foot-pounds.  Remember  that  no  work  can  be  done  by  a  force 
unless  it  succeeds  in  producing  motion.  A  man  might  tug  all 
day  at  a  weight  but  unless  he  succeeded  in  raising  it  he  would 
do  no  work.  Likewise  if  the  pressure  on  the  piston  of  a  steam 
engine  is  not  great  enough  to  overcome  the  load  and  turn  the 
engine,  there  will  be  no  work  done. 

50.  Power. — Power  is  the  rate  of  doing  work.     To  lift  a  stone 
weighing  10,000  lb.  to  a  height  of  7  ft.  will  require  70,000  foot- 
pounds of  work.     If  one  hoisting  engine  can  do  this  in  half  the  time 
that  another  one  can,  the  first  engine  is  twice  as  powerful  because 
it  must  do  the  work  twice  as  fast.     We  see,  then,  that  in  calcu- 
lating power,  time  must  be  considered.     The  engine  which  can 
do  the  most  work  in  a  minute  has  the  greatest  power. 

51.  Horse-power. — The  engineer's  standard  of  power  is  the 
horse-power.     This  standard  was  established  by  James  Watt, 
who  estimated  that  an  average  horse  was  able  to  work  con- 
tinuously at  the  rate  of  33,000  foot-pounds  per  minute.     One 
horse-power  is  therefore  a  rate  of  working  of  33,000  foot-pounds 
per  minute  (or  550  foot-pounds  per  second). 

If  a  force  of  18,000  lb.  is  required  to  move  a  train  of  30  cars,  the 
work  required  to  move  it  1  mile  will  be  18,000X5280  =  95,040,000 
foot-pounds.  An  engine  that  could  do  this  in  2  minutes  would 
do  95,040,000-^-2  =  47,520,000  foot-pounds  per  minute;  and  its 
horse-power  would  be  47,520,000-^-33,000  =  1440  horse-power. 
If  another  engine  required  4  minutes  to  haul  the  train  1  mile  it 
would  only  do  half  as  much  work  in  a  minute  and  its  horse- 
power would  be  only  half  as  great,  or  720  horse-power. 

52.  Energy. — Energy    is    ability  to  do  work.     Heat  can  be 
made  to  do  work  through  a  steam  engine  or  gas  engine  and, 
therefore,   heat  is-  energy.     Electricity   also   can  do   work  by 
means   of   an  electric :  motor;   therefore,   electricity  is  energy. 
The  energy  of  a  body  in  motion,  as,  for  instance,  the  energy 
of  a  revolving  flywheel  is  called  mechanical  energy.     Light  is 
still  another  form  of  energy,  because  we  can  turn  heat  or  elec- 
tricity into  light  and,  if  they  are  forms  of  energy,  light  must 
also  be  energy.     The  various  forms  of  energy  with  which  we 
may  have  to  deal  in  a  power  plant  are:  heat,  mechanical  energy, 
electricity,  and   light.     Heat   is   liberated   from   the   coal   and 
given  to  the  water  in  forming  steam;  the  engine  takes  heat  from 


HEAT  AND  WORK  75 

the  steam  and  changes  it  to  mechanical  energy;  the  dynamo 
changes  this  mechanical  energy  to  electricity;  the  electricity  is 
transmitted  through  wires  to  some  distant  point  and  there  trans- 
formed to  heat  and  light  by  electric  lamps,  or  to  mechanical 
energy  by  an  electric  motor. 

Energy  cannot  be  destroyed  nor  created  but,  as  has  been 
shown,  can  be  readily  changed  from  one  form  to  another. 
There  are  many  cases  where  it  appears  on  first  thought  as  if 
energy  were  lost  but  on  close  examination  we  find  that  such  is 
not  the  case.  In  a  long  line  shaft  we  may  not  get  as  much 
mechanical  energy  at  one  end  as  was  put  in  at  the  other  end  but 
we  find  that  what  has  apparently  been  lost  has  really  been 
changed  into  heat  in  overcoming  the  friction  of  the  bearings. 
The  mechanical  energy  expended  in  cutting  a  piece  of  steel  is 
also  changed  to  heat  and  we  find  that  the  steel  and  also  the 
tool  used  will  become  warmer  during  the  process. 

53.  Heat. — Although  heat  and  its  effects  have  been  observed 
and  studied  for  many  hundreds  of  years  it  was  only  in  the  past 
century  (the  nineteenth)  that  scientists  completely  formu- 
lated our  present  theory  as  to  its  nature  and  effects.  Formerly 
heat  was  supposed  to  be  an  actual  substance  which  entered  a 
body  when  that  body  became  hot,  and  left  it  when  it  became  cold. 
We  now  believe  heat  to  be  a  form  of  energy  which  can  be  changed 
to  work,  electricity,  or  any  of  the  other  forms  of  energy.  These 
changes  of  form  can  be  seen  in  numerous  cases,  some  of  which 
have  already  been  mentioned. 

It  is  generally  accepted  that  heat  exists  in  bodies  as  a  very 
rapid  invisible  motion  of  the  fine  particles  or  molecules  of  the 
bodies.  Each  particle  is  supposed  to  have  a  violent  to-and-fro 
motion  and  the  greater  the  amount  of  heat  energy  in  a  body 
the  greater  must  be  the  energy  of  each  molecule  and,  hence, 
the  greater  will  be  the  rapidity  of  this  molecular  motion.  The 
application  of  this  theory  can  be  extended  to  all  of  the  phenomena 
of  heat.  For  example,  the  melting  of  solids  into  liquids  and  the 
evaporation  of  liquids  into  gases  is  explained  as  follows:  There 
is  a  force  of  attraction  known  as  cohesion  which  tends  to  hold 
the  particles  of  any  substance  together  and  which,  in  a  solid, 
is  strong  enough  to  hold  the  body  in  a  certain  shape.  Heat 
causes  the  particles  to  move  to  and  fro  and  thus  exerts  a  force 
opposite  to  cohesion,  tending  to  separate  the  particles.  As  heat 
is  applied  and  the  particles  are  separated  the  force  of  cohesion 


76  STEAM  BOILERS 

acts  more  and  more  feebly  until  finally  the  particles  are  able  to 
move  among  each  other,  though  still  held  together  slightly. 
This  is  the  liquid  state.  As  the  liquid  is  further  heated  a  point 
is  reached  where  the  motion  of  the  particles  becomes  so  great 
that  they  will  tend  to  fly  apart  and  try  to  separate.  Cohesion 
is  then  entirely  overcome  and  we  have  a  gas. 

54.  Energy  of  Fuels. — When  a  fuel  is  burned,  it  brings  into 
existence  a  certain  amount  of  heat.     This  energy  must  exist  in 
the  fuel  in  some  form  before  combustion  occurs,  if  we  are  to 
believe  that  energy  cannot  be  created  or  destroyed.     We  know 
that  prior  to  combustion  the  energy  of  the  coal  is  not  heat  and  yet 
the  only  way  we  can  make  it  available  for  use  is  to  turn  it  into 
heat.     Consequently,   we   often   designate   it  by  the  name   of 
"Potential  Heat."     "Fuel  Energy"  and  " Chemical  Energy,"  are 
other  names  that  can  be  rightly  applied  to  energy  in  this  form; 
but,  since  in  our  work  we  think  of  it  only  as  "stored  up"  heat 
and  use  it  only  after  turning  it  into  the  heat  form,  we  will  use 
the  term  Potential  Heat.     If  we  investigate  the  origin  of  our 
natural  deposits  of  fuels,  such  as  coal,  petroleum,  and  natural 
gas,  we  can  readily  understand  the  idea  of  fuel  energy  being 
"stored  up"  heat.     The  sun  is  the  source  of  all  our  heat  energy 
and  all  the  daily  manifestations  of  energy,  as  in  wind  or  water 
powers  or  the  heat  from  a  fire,  are  but  exhibitions  of  energy 
that  came  originally  from  the  sun.     Because  of  the  sun's  heat 
forests  grow  and  give  us  wood  for  fuel.     In  a  similar  manner 
the  coal  was  formed  ages  ago.     The  earth's  surface  was  at  one 
time  covered  with  a  dense  growth  of  vegetation,  which  became 
covered  with  rock  and  soil,  and,  by  the  action  of  heat  and  pres- 
sure, this  vegetation  underwent  a  gradual  change  until  we  find 
it  at  present  in  the  form  of  coal. 

55.  Sensible  and  Latent  Heat. — The  first  impression  we  get  of 
heat  is  that  caused  by  its  effect  on  our  sense  of  feeling.     We 
touch  an  object  and  say  that  it  is  hot  or  cold  according  to  its 
effect  on  our  senses.     Heat  which   can  thus  be   felt  is  callqd 
"  Sensible  Heat."     But  heat  can  exist  in  other  forms  not  notice- 
able to  our  sense  of  feeling.     When  we  melt  a  piece   of  ice, 
considerable  heat  is  required  to  make  the  change,  and  yet  the 
ice   water  formed,  is  just   as  cold   as    the   ice.     Similarly,  the 
steam  formed  when  we  boil  water  is  no   hotter  than  the  water 
which  is  boiling,  but  a  large  amount  of  heat  is  required  to  change 
the  water  into  steam.     Heat  which  is  thus  utilized  in  chang- 


HEAT  AND  WORK  77 

ing  the  state  of  a  substance  without  effecting  any  change  of 
temperature  is  called  "Latent  Heat." 

56.  Temperature. — The  impression  which  sensible  heat  makes 
on  our  senses  we  call  temperature.     Temperature  is  a  measure 
of  the  intensity  of  heat  in  a  body.     It  is  not  true,  as  is  often  said, 
that  temperature  indicates  the  amount  of  heat.     A  quart  of  water 
may  have  more  heat  than  a  pint  of  water  and  yet  be  colder.     A 
pound  of  iron  will  have  far  less  heat  than  a  pound  of  water  at 
the  same  temperature,  because  water  has  a  greater  capacity 
for  heat  than  iron.     Likewise  a  pound  of  ice  water  will  contain 
more  heat  than  a  pound  of  ice  although  they  will  be  at  the  same 
temperature. 

57.  Measuring  Temperatures. — The  common  method  of  meas- 
uring temperature  is  by  means  of  an  instrument  known  as  a 
thermometer,  which  usually  consists  of   a  glass  tube  partially 
filled  with  mercury  or  some  other  substance  which  will  expand 
or  contract  as  the  temperature  rises  or  falls  and  thus  will  indicate 
the  temperature. 

58.  Thermometer  Scales. — There  are  two  kinds  of  thermo- 
meter scales  in  common  use;  the  Centigrade,  abbreviated  C., 
and  the  Fahrenheit,  abbreviated  Fahr.  or  F.     On  the  Centigrade 
thermometer  the  space  between  the  freezing-point  of  water  and 
the  boiling-point  at  atmospheric  pressure  is  divided  into  100 
equal  parts  called  degrees,  the  freezing-point  being  marked  zero 
(0)  and  the  boiling-point  100°.     The   balance  of   the   scale  is 
then  divided  into  spaces  of  equal  length  below  zero  and  above 
100°  in  order  that  temperatures  higher  than  100°  and  lower  than 
zero  may  be  read. 

On  the  Fahrenheit  scale  the  freezing-point  of  water  is  marked 
32°  and  the  boiling-point  212°,  and  the  space  between  is  divided 
into  180  degrees.  This  scale  is  also  marked  with  divisions 
below  32°  and  above  212°  in  order  to  make  the  thermometer 
read  through  a  wider  range.  The  Fahrenheit  thermometer  is 
used  more  commonly  in  the  United  States  than  the  Centigrade, 
which  is  used  extensively  in  Europe.  In  this  work  the  Fahren- 
heit scale  will  be  used  exclusively  and  where  temperatures  are 
given  without  any  reference  to  the  scale  it  will  be  understood 
to  be  the  Fahrenheit. 

In  Fig.  57  the  two  scales  are  shown  side  by  side  and  the 
student  can  see  at  a  glance  the  relation  between  them.  Since 
the  same  interval  of  temperature  is  divided  into  100  parts  in  the 


78 


STEAM  BOILERS 


Centigrade  scale  and  180  parts  in  the  Fahrenheit  scale  the 
Centigrade  degree  is  ^^  or  ^  of  the  Fahrenheit  degree.  Simi- 

1UU  O 

larly,  the  Fahrenheit  degree  is  five-ninths  of  the  Centigrade  de- 
gree. In  changing  a  reading  on  one  thermometer  to  the  corre- 
sponding reading  on  the  other  it  must  be  borne  in  mind  that 


210" 

200— 

100— 

130— 

170— 

130— 

150  — 

140— 

130— 

120— 

110— 

'100— 

90— 


20— 

10— 

0— 

-10— 

-20— 

-30— 

-40— 


T12  F=  100  C 


—  20 

—  10 

—  o°c 

10 

20 

30 

—40 


FIG.  57. 


their  zeros  are  not  at  the  same  point  but  are  32  Fahrenheit 
degrees  apart. 

Hence:  To  reduce  from  the  Fahrenheit  to  the  Centigrade  scale, 
first  find  how  many  Fahrenheit  degrees  the  given  temperature  is 
above  or  below  freezing  and  then  multiply  this  by  five-ninths. 

To  reduce  from  the  Centigrade  to  the  Fahrenheit  scale,  first 
I  tiply  by  nine-fifths  to  find  how  many  Fahrenheit  degrees  the 


HEAT  AND  WORK  79 

given  temperature  is  above  or  below  freezing.  Then  make  the 
necessary  change  for  the  fact  that  the  Fahrenheit  zero  is  thirty-two 
Fahrenheit  degrees  below  freezing. 

These  rules  may  be  stated  briefly  by  the  following  formulas  : 


where  F  represents  degrees  above  zero  Fahrenheit  and 

C  represents  the  corresponding  reading  above  zero  Centi 
grade.     Thus  if  it  is  desired  to  change  26°  C.  to  F.  : 


=  46.8  +  32-78.8 

Hence  26°  C.=  78.8°  F. 

Likewise  to  change  170°  F.  to  Centigrade  we  have: 


-138X^  =  76.6  + 

Hence  170°  F.  =76.6°+  C. 

Many  people  make  the  mistake  of  adding  or  subtracting  the 
number  32  in  cases  where  they  should  not.  For  example,  sup- 
pose the  mercury  in  a  Centigrade  thermometer  rises  20  degrees  on 
a  certain  day  and  we  want  to  find  the  equivalent  rise  in  Fahrenheit 
degrees.  Each  degree  on  the  C.  scale  equals  nine-fifths  degree 
on  the  F.  scale. 


Hence  a  Fahrenheit  thermometer  would  show  a  rise  of  36°  on 
the  same  day.  In  this  case  the  fact  that  the  zero  points  are  not 
the  same  has  no  connection  with  the  problem,  since  we  are 
dealing  only  with  changes  in  temperature  and  not  with  readings 
from  the  zero  points. 

59.  Thermometers  and  Pyrometers.  —  Mercury  freezes  at  39° 


80  STEAM  BOILERS 

below  zero  Fahrenheit  ( —39°  F.)  and  consequently  cannot  be 
used  for  temperatures  below  this  point.  Temperatures  lower 
than  this  -are  usually  measured  with  thermometers  containing 
alcohol,  since  the  freezing-point  of  alcohol  is  —202°  F. 

As  mercury  boils  at  680°  F.  it  is  not  suitable  for  use  in  ther- 
mometers which  are  to  indicate  very  high  temperatures  and  for 
this  purpose  other  devices  must  be  used.  Such  devices  are  called 
pyrometers.  As  the  mercury  thermometer  is  ordinarily  made,  it 
should  not  be  used  for  temperatures  above  500°,  but  byjfilling  the 
glass  tube  above  the  mercury  with  an  inactive  gas,  such  as  nitro- 
gen, under  high  pressure  the  boiling-point  of  the  mercury  will 
be  raised  and  a  thermometer  can  be  made  that  may  be  read  up 
to  900°.  Constructed  in  this  way  it  forms  one  of  the  best  instru- 
ments for  determining  stack  temperatures  in  boiler  plants. 

Devices  for  indicating  very  high  temperatures  are  called 
Pyrometers.  One  of  the  simplest  forms  of  pyrometer  depends 
for  its  operation  on  the  fact  that  some  metals  expand  more  than 
others  when  heated  to  the  same  temperature.  It  is  well  known 
that  a  metal  rod  will  expand  when  it  is  heated.  Brass  will 
expand  much  more  than  iron  and  this  difference  in  expansion 
can  be  used  to  indicate  temperatures.  In  form,  such  a  py- 
rometer looks  like  an  ordinary  steam  gage  with  a  straight  piece 
of  pipe  about  2  ft.  long  connected  to  it.  The  pipe  is  closed  at 
the  outer  end  and  contains  a  brass  or  copper  rod,  one  end  of 
which  is  fastened  to  the  outer  end  of  the  pipe.  The  other  end 
is  connected  by  a  suitable  mechanism  to  a  hand  on  the  dial  of 
the  instrument.  As  the  tube  and  rod  are  heated,  the  difference 
in  expansion  causes  the  hand  to  move  over  the  dial,  which  is 
graduated  to  read  in  degrees. 

In  order  to  obtain  an  accurate  determination  of  the  tempera- 
ture the  iron  and  brass  must  be  at  the  same  temperature  through- 
out their  lengths.  The  difficulties  of  securing  this  and  of  avoiding 
lost  motion  in  the  gears  make  this  form  of  pyrometer  somewhat 
unreliable.  A  peculiarity  of  these  expansion  pyrometers  is  that 
when  the  temperature  starts  to  fall,  the  pointer  will  move  up 
and,  also,  when  the  temperature  starts  to  rise  the  pointer  will 
move  backward.  This  is  because  the  brass  strip  is  enclosed  in 
an  iron  tube  and  the  heat  affects  the  iron  before  it  does  the 
brass.  As  soon  as  the  heat  penetrates  to  the  brass  and  a  uniform 
temperature  is  attained  the  pointer  will  take  up  its  correct 
position. 


HEAT  AND  WORK 


81 


23    | 


c™::::;:, 

ss*™,^ 

j_ 

FIG.  58. — Le  Chatelier  pyrometer. 


FIG.  59. — Clay  cone  pyrometer. 


82  STEAM  BOILERS 

Another  form  of  pyrometer,  far  more  delicate  than  the  above, 
is  one  called  the  Le  Chatelier.  It  is  made  by  joining  two  dis- 
similar metals  and  connecting  the  joint  to  a  galvanometer  by 
wires.  Such  a  joint  has  the  property,  when  heated,  of  gen- 
erating a  current  of  electricity,  and  the  strength  of  the  current 
is  proportional  to  the  temperature  of  the  joint.  The  galva- 
nometer measures  the  strength  of  the  current  and  thus  indicates 
the  temperature  of  the  joint.  It  may  be  placed  at  a  distance 
from  the  point  where  the  heat  is  applied  and  is,  therefore,  a 
very  convenient  instrument  for  certain  cases.  The  joints,  or 
elements  as  they  are  called,  are  enclosed  in  porcelain  tubes  to 
protect  them  from  injury.  The  metals  used  in  making  these 
pyrometers  are  usually  platinum  and  an  alloy  of  platinum  and 
rhodium.  These  metals  will  stand  exceedingly  high  tempera- 
tures, but  for  such  work  are  usually  protected  by  porcelain  or 
clay  tubes.  When  constructed  in  this  manner  these  pyrometers 
can  be  used  for  taking  the  temperatures  of  furnaces  or  of  molten 
metals.  A  Le  Chatelier  pyrometer  is  shown  in  Fig.  58. 

Another  common  method  of  determining  furnace  temperatures 
is  by  the  use  of  small  cones  of  clay  composition  such  as  shown 
in  Fig.  59.  The  composition  of  these  cones  is  such  that  they  will 
melt  at  certain  known  temperatures.  By  placing  in  a  furnace 
a  number  of  these  cones  having  different  melting-points  and  by 
observing  which  ones  melt  and  which  stand  erect  we  can  tell 
very  closely  the  temperature  within  the  furnace.  The  dealers 
in  these  cones  furnish  with  them  a  table  of  temperatures  at 
which  they  melt. 

High  temperatures  can  be  judged  approximately  by  color  but 
the  results  will  depend  on  the  eye  of  the  observer  and  on  the 
degree  of  illumination  under  which  the  observations  are  made. 
A  piece  of  steel  that  would  be  red-hot  in  a  darkened  room 
would  be  black-hot  in  broad  daylight.  The  following  table  from 
Kent's  Handbook  gives  the  colors  and  their  corresponding 
temperatures : 

Color  Degree  F. 

Incipient  red  heat 977 

Dull  red  heat 1292 

Incipient  cherry-red  heat 1472 

Cherry-red  heat 1652 

Clear  cherry-red  heat 1832 


HEAT  AND  WORK  83 


Color  Degree  F. 


Deep  orange  heat. . . 
Clear  orange  heat. . . 

White  heat 

Bright  white  heat.  . 
Dazzling  white  heat 


60.  The  Unit  of  Heat. — The  most  common  way  of  measuring 
heat  is  to  observe  its  effect  in  raising  the  temperature  of  a  quantity 
of  water.  Consequently,  it  is  but  natural  that  we  should  take 
as  our  unit  of  heat  the  quantity  of  heat  that  is  necessary  to 
raise  the  temperature  of  1  Ib.  of  water  1  degree  on  the  Fahren- 
heit thermometer.  This  unit  is  called  the  British  Thermal  Unit 
(B.t.u.)  and  it  is  most  often  designated  simply  by  the  letters 
B.t.u.  instead  of  by  the  full  name.  The  quantity  of  heat 
required  to  raise  the  temperature  of  a  pound  of  water  1  degree 
is  not  exactly  the  same  at  different  temperatures  and  for  this 
reason  it  is  necessary  to  specify  the  temperatures  at  which  the 
B.t.u.  is  denned.  To  be  exact,  we  have  taken  as  1  B.t.u.  the 
amount  of  heat  required  to  change  the  temperature  of  1  Ib.  of 
pure  water  from  62°  F.  to  63°  F.,  these  temperatures  being  used 
because  they  are  easily  obtained.  As  a  general  rule  it  is  suffi- 
ciently accurate  to  figure  that  1  B.t.u.  is  transferred  when  a 
pound  of  water  is  raised  1  degree  at  any  ordinary  temperature. 
If  7  Ib.  of  water  are  heated  through  5  degrees  the  heat  given  to 
the  water  is  the  product  of  7  and  5  or  35  B.t.u. 

The  method  used  to  determine  the  heating  value  of  coal  is 
to  burn  a  small  sample  so  that  the  heat  will  all  be  given  to  a 
certain  known  quantity  of  water.  By  observing  the  change  in 
the  temperature  of  the  water  the  heat  can  be  calculated.  The 
apparatus  used  for  this  purpose  is  called  a  calorimeter.  Suppose 
we  burned  .003  Ib.  of  coal  in  a  calorimeter  and  find  that  it  heats 
7  Ib.  of  water,  causing  a  rise  in  temperature  of  6°  F.  The  heat 
given  to  the  water  is 

7X6  =  42  B.t.u. 

This  heat  came  from  only  .003  Ib.  of  the  coal  so  1  Ib.  of  the  coal 
would  therefore  yield 

42  -=-.003  =  14,000  B.t.u. 


84  STEAM  BOILERS 

61 .  Relation  of  Heat  and  Work. — Since  heat  and  work  are  both 
forms  of  energy,  there  must  be  some  definite  relation  between 
the  units  of  heat  and  of  work,  that  is,  between  the  B.t.u.  and 
the  foot-pound.     It  has  been  found  by  actual  experiment  that, 
if  a  quantity  of  work  is  tranformed  into  heat,  it  requires  778 
foot-pounds  to  give  1  B.t.u.     On  the  other  hand,  if  1  B.t.u.  is 
entirely  transformed  to  work  it  will  give  778  foot-pounds.     This 
quantity  (778)  is  what  is  termed  "  The  Mechanical  Equivalent 
of  Heat"   and   also   is   sometimes   called   "Joules   Equivalent" 
because  Joule  was  the  first  to  establish  a  relation  between  these 
quantities.     The   value  found   by   Joule    (772)    was,   however, 
afterward  proved  to  be  too  low. 

As  an  example  of  this  relation  let  us  take  the  case  of  an  engine 
that  loses  10  h.p.  in  friction.  Since  1  h.p.  equals  33,000  foot- 
pounds a  minute  this  engine  will  lose  330,000  foot-pounds  a 
minute  in  friction.  This  work  that  is  lost  in  friction  is  really 
turned  into  heat  and,  since  330,000  foot-pounds  =  330,000-^778 
=  424  B.t.u.,  we  find  that  the  heat  generated  in  the  bearings 
and  rubbing  surfaces  of  this  engine  amounts  to  424  B.t.u.  per 
minute. 

It  is  impossible  for  an  engine  to  receive  a  quantity  of  heat  and 
transform  all  of  it  into  work.  A  steam  engine  receives  heat 
in  the  steam  and  transforms  part  of  this  heat  into  work  but  the 
exhaust  from  the  engine  carries  off  a  large  percentage  of  the 
heat  that  is  supplied.  If  an  engine  were  able  to  transform  all 
of  the  heat  it  receives  into  work  we  would  only  need  to  supply 
33,000^778=42.42  B.t.u.  per  minute  for  each  horse-power, 
or  2545  B.t.u.  per  hour  per  horse-power.  The  best  steam  engines 
only  transform  into  work  about  20  to  25  per  cent  of  the  heat 
supplied  them  and  many  can  do  no  better  than  4  or  5  per  cent. 

62.  Heat  Cycle  of  a  Steam  Power  Plant. — A  study  of  the  heat 
diagram  shown  in  the  lower  part  of  Fig.  56  will  show  what  becomes 
of  the  heat  supplied  in  the  form  of  fuel  to  the  boiler  furnace. 
In  this  diagram  the  small  branches  which  lead   off  from  the 
main  diagram  show  the  various  losses,  while  those  branches 
which  return  to  the  main  diagram  show  the  portions  of  heat 
that  are  saved. 

If  we  consider  a  single  pound  of  fuel  having  a  heating  value 
of  13,500  B.t.u.  fed  into  the  furnace,  the  first  loss  of  heat  occurs 
by  unburned  fuel  dropping  through  the  grate,  amounting  to 
about  1  per  cent  or  135  B.t.u.  out  of  the  total  of  13,500.  It 


HEAT  AND  WORK  85 

must  be  understood  that  all  of  the  values  given  in  this  diagram  are 
only  approximate,  and  will  vary  with  different  plants.  They 
are  given  here  simply  to  indicate  in  a  general  way  the  amount  of 
heat  lost  in  various  ways. 

The  remainder  of  the  heat  which  leaves  the  grate,  amounting 
to  about  99  per  cent,  divides,  about  72  per  cent  passing  into 
the-boiler  and  the  remaining  27  per  cent  or  2970  B.t.u.  passing 
out  of  the  chimney  in  the  hot  flue  gases.  The  heat  which  passes 
into  the  boiler  heats  the  water  and  forms  steam  and  also  heats 
the  shell,  which  radiates  some  heat  to  the  atmosphere.  This 
amounts  to  about  5  per  cent  of  the  total,  or  675  B.t.u. 

The  remaining  72  per  cent  of  the  heat  is  carried  into  the  pipes 
by  the  steam.  About  1.78  per  cent  or  240  B.t.u.  is  lost  by 
radiation  from  the  hot  pipes  and  the  remainder  passes  on  to  the 
engine.  Here  another  2.08  per  cent  or  280  B.t.u.  are  lost  by 
radiation  from  the  heated  portions  of  the  engine, while  about  9.43 
per  cent  or  1273  B.t.u.  are  turned  into  work  in  the  cylinder. 
Not  all  of  this  9.43  per  cent  is  in  the  form  of  useful  work,  however, 
as  about  1  per  cent  is  used  to  overcome  the  friction  in  the  moving 
parts  of  the  engine.  The  remainder,  8.43  per  cent  or  1138  B.t.u. 
is  delivered  to  the  flywheel  in  the  form  of  useful  work.  This 
may  seem  like  a  very  small  portion  of  the  total  heat  to  be 
utilized,  yet  it  is  as  much  as  may  be  expected  under  the  ordi- 
nary conditions. 

The  larger  part  of  all  the  heat,  amounting  to  about  57.31  per 
cent  or  7738  B.t.u.,  passes  out  of  the  engine  in  the  exhaust  with- 
out doing  any  useful  work.  All  of  this  would  be  lost  if  the 
engine  was  run  non-condensing,  but  in  the  power  plant  shown 
here,  the  exhaust  steam  is  condensed  and  this  furnishes  a  supply 
of  hot  feed  water.  By  doing  this,  about  4  per  cent  or  540  B.t.u. 
is  saved  and  returned  to  the  boiler.  The  remaining  53.31  per 
cent  or  7197  B.t.u.  passes  off  in  the  hot  circulating  water  from 
the  condenser  and  is  lost. 

The  feed  pump  also  takes  about  1.4  per  cent  or  190  B.t.u.  and 
of  this,  uses  about  0.4  per  cent  or  54  B.t.u.  to  pump  the  water, 
while  the  remainder,  1  per  cent  or  135  B.t.u.  may  be  used  to 
further  heat  the  feed  water  and  thus  be  saved.  This  accounts 
for  all  the  heat  supplied  to  the  grates.  These  various  losses  are 
tabulated  below. 


86  STEAM  BOILERS 

WHAT  BECOMES  OF  THE  HEAT   IN  THE  COAL 

Lost  through  the  grates 1 . 00  per  cent  135  B.t.u. 

Lost  by  radiation  from  boiler 5. 00  per  cent  675  B.t.u. 

Lost  in  chimney  gases 22.00  per  cent  2970  B.t.u. 

Lost  by  radiation  from  pipes 1 . 78  per  cent  240  B.t.u. 

Delivered  to  pumps 1 .40  per  cent  190  B.t.u. 

Lost  by  radiation  from  engine 2.08  per  cent  280  B.t.u. 

Lost  in  engine  friction 1 . 00  per  cent  135  B.t.u. 

Lost  in  engine  exhaust 57.31  per  cent  7738  B.t.u. 

Useful  work  delivered  to  iiy  wheel 8.43  per  cent  1137  B.t.u. 


100.00  per  cent      13500  B.t.u. 


CHAPTER  VI 
EFFECTS  OF  HEAT 

63.  Expansion  of  Solids. — Nearly  all  substances  expand  when 
heat  is  applied  to  them  and  contract  when  heat  is  removed. 
This  phenomenon  is  greatest  in  gases  and  least  in  solids,  but 
even  in  solids  is  of  enough  moment  so  that  it  must  be  considered 
in  the  design  and  installation  of  boilers. 

When  a  solid  body  is  heated  it,  of  course,  expands  in  all 
directions  if  free  to  do  so;  but,  as  a  rule,  we  are  concerned  only 
with  the  change  of  one  dimension  and  not  with  the  change  in 
volume.  Thus,  in  the  case  of  a  steam  pipe,  we  do  not  care 
especially  about  the  change  in  thickness  or  in  diameter  but 
we  are  concerned  with  the  change  in  length. 

The  amount  of  linear  expansion  which  a  body  undergoes 
depends  upon  the  kind  of  material,  upon  the  amount  of  the 
temperature  change  and,  of  course,  upon  the  original  length. 

64.  Coefficients    of    Expansion. — The  Coefficient    of    Linear 
Expansion  of  a  substance  is  that  part  of  its  original  length  which 
a  body  will  expand  for  each  degree  change  in  temperature. 
Coefficients  for  different  metals  have  been  determined  for  our 
use  by  careful  experiments  and  can  be  found  in  handbooks  or 
tables  under  the  head  of  "  Coefficients  of  Expansion."     A  few 
of  the  most  common  are  given  here: 

COEFFICIENTS  OF  EXPANSION 


Metal 

Coefficient 

Aluminum    . 

00001234 

Brass  

.00001 

Cast  iron  

Wrought  iron  and  machine  steel  
36  per  cent  nickel  steel          .          .    . 

.  0000055  to 
.  000006 
.0000065 
.  0000003 

87 


88  STEAM  BOILERS 

The  above  values  are  based  on  a  temperature  rise  of  1°  F.  For 
1  Centigrade  degree  the  coefficients  would  be  9/5  of  those  just 
given.  The  student  is  not  expected  to  memorize  these  values. 
Where  exact  calculations  are  not  necessary  the  value  "  five  zeros- 
six"  (.000006)  for  cast  iron  can  be  easily  carried  in  mind.  For 
steel  or  wrought  iron  annex  a  5,  making  it  .0000065.  For  copper, 
brasses,  and  bronzes  a  value  of  "four  zeros-one"  (.00001)  is 
easily  carried  in  mind.  Remember  that  if  the  length  is  given 
in  feet  the  expansion  calculated  will  be  in  feet  and  if  the  length 
is  in  inches  the  expansion  will  be  obtained  in  inches.  The 
increase  in  length  of  a  body  due  to  expansion  may  be  expressed 
by  the  following  formula: 

e  =  tC  L 
where     e  is  the  change  in  length 

1    t  is  the  change  in  temperature 

C  is  the  coefficient  of  linear  expansion 
L  is  the  original  length  of  the  body. 

The  same  formula  applies  to  contraction  when  a  body  is  cooled. 
Example :  What  will  be  the  expansion  of  a  steam  pipe  200  ft. 
long  when  subjected  to  a  temperature  of  300°,  if  erected  when  the 
temperature  was  60°?  Note:  The  pipe  used  for  steam  lines  is 
generally  of  steel  though  some  people  prefer  wrought  iron  when 
it  can  be  obtained. 

Solution:  The  change  in  temperature  is  300-60  =  240°  and 
the  coefficient  for  steel  is  .0000065 

e  =  240  X.  0000065X200 
=  .312  ft.  or  3f  in.,  nearly. 

A  good  working  knowledge  of  the  effect  of  heat  on  metals  is 
of  great  importance  to  the  engineer.  A  failure  to  provide  for  ex- 
pansion in  steam  piping  has  caused  many  leaks  and  some  serious 
accidents.  In  turbine  work,  change  in  position  of  parts  due  to 
heating  will  seriously  affect  the  alignment.  The  erecting  engi- 
neer makes  use  of  expansion  and  contraction  when  putting  links 
in  a  flywheel  rim  or  shrinking  bolts  in  the  hub.  In  setting  a 
boiler,  provision  must  be  made  for  expansion  and  contraction. 

65.  Expansion  of  Liquids. — The  expansion  of  mercury  and 
alcohol  under  increase  of  temperature  has  already  been  referred 
to  under  the  discussion  of  thermometers.  Water  also  expands 
when  heated,  except  as  follows :  A  given  weight  of  water  occupies 


EFFECTS  OF  HEAT 


89 


the  least  volume  at  39.2°  F.  and  if  cooled  below  this  tempera- 
ture will  expand  until  it  freezes  at  32°  F.  The  density  of  water 
is,  therefore,  the  greatest  at  39.2°  F.  As  a  very  important  result 
of  this,  we  note  that  ice  forms  on  the  surface  of  water  because 
after  water  is  cooled  below  39.2°  the  coldest  water  will  rise  to 
the  surface  and  the  warmest  will  descend. 

66.  Expansion  of  Gases. — Gases  likewise  will  expand  when 
heated.  However,  an  added  complication  is  introduced  in  con- 
sidering the  expansion  of  gases,  owing  to  the  fact  that  the 
volume  of  a  gas  is  readily  reduced  by  increasing  the  pressure  on 


FIG.  60. 

it  and  is  increased  by  reducing  the  pressure.  Fig.  60  shows  a 
certain  weight  of  gas  held  within  the  cylinder  and  maintained 
at  a  certain  pressure  by  the  weights  W.  If  we  remove  part  of 
the  weights,  the  pressure  on  the  gas  will  be  reduced,  the  gas 
will  force  the  piston  upward,  and  the  volume  will  increase 
accordingly. 

In  studying  the  effect  of  heat  on  gases,  let  us  imagine  that 'a 
flame  is  applied  to  the  bottom  of  the  cylinder  in  Fig.  60.  The 
gas  will  be  heated  and,  as  the  energy  of  the  particles  of  the  gas 
is  thus  increased,  they  tend  to  vibrate  in  a  wider  space  and 


90  STEAM  BOILERS 

thus  the  gas  expands  and  raises  the  piston  and  occupies  a  larger 
volume.  In  this  case,  the  gas  has  been  heated  "at  constant 
pressure"  (the  weights  remaining  the  same)  and  it  will  be  found 
that  gases  so  heated  obey  a  regular  law  in  expanding.  It  is  of 
course  possible,  by  fastening  the  piston  or  by  adding  weights 
gradually,  to  prevent  the  volume  from  increasing  as  the  tem- 
perature is  increased.  In  this  case  the  gas  is  heated  "at  con- 
stant volume"  and  the  pressure  increases  regularly  as  the 
temperature  rises. 

67.  Absolute  Zero.  —  By  experiment  it  has  been  found  that  1 
cu.  ft.  of  a  gas  at  32°  will  expand  to  1.366  cu.  ft.  when  heated  to 
212°  under  a  constant  pressure.  This  means  that  for  each  degree 

,    .366       1       .  .,        .  .     , 
rise  in  temperature  the  gas  expands  ^TO    —  TO  °^  ^s  ongmal 


volume  at  32°  F.  and  we  find  that  this  expansion  is  uniform 
throughout  the  range  of  temperature.  Now,  let  us  imagine  what 
would  happen  if  this  cubic  foot  of  gas  were  cooled  below  32°  F. 

At  0°  F.  it  would  occupy  only  -.   ^  cu.  ft.  and  if  the  temperature 


could  be  reduced  to  460°  below  zero  the  gas  would  have  no 
volume  whatever.  This  means  that,  according  to  our  theory  of 
heat,  the  heat  energy  has  been  entirely  removed  and  the  par- 
ticles cease  to  vibrate  and,  therefore,  that  -460°  F.  is  the  lowest 
possible  temperature  and  is  absolute  zero.  As  a  matter  of  fact 
the  different  gases  all  liquefy  before  this  temperature  is  reached, 
but  scientists  have  reached  as  low  as  -436°  F.  Air  liquefies  at 
about  -300°  F. 

Absolute  temperature  is  temperature  calculated  above  absolute 
zero  and  is  obtained  by  adding  460  to  the  reading  on  the  ordinary 
Fahrenheit  thermometer.  Thus  40°  F.  equals  40  +  460-500 
degrees  absolute. 

It  has  been  shown  above  that,  when  a  gas  is  heated  or  cooled 
while  the  pressure  remains  constant,  its  volume  increases  or  de- 
creases in  proportion  to  its  absolute  temperature.  If  the  cylin- 
der mentioned  above  had  contained  1  cu.  ft.  of  gas  at  a  tempera- 
ture of  70°  F.  or  530°  absolute,  and  had  been  heated  at  constant 
pressure  to  300°  F.  or  760°  absolute,  its  volume  would  have 

increased  to  lX^™  =  1.43  cu.  ft. 

OoU 

//  a  gas  is  heated  while  its  volume  remains  constant,  its  pressure 
will  increase  or  decrease  in  proportion  to  its  absolute  temperature. 


EFFECTS  OF  HEAT 


91 


Thus  if  a  certain  volume  of  gas  at  a  temperature  of  60°  F.  or 
520°  absolute  and  a  pressure  of  100  Ib.  per  square  inch  is  heated 
at  constant  volume  to  200°  F.  or  660°  absolute  its  pressure  will 
increase  to 


=  127  Ib.  per  square  inch. 


68.  Transmission  of  Heat.  —  One  of  the  most  important  things 
in  studying  heat  in  connection  with  steam-boiler  operation  is  the 
manner  of  transferring  heat  from  one  body  to  another.     There 
are  three  methods  of  heat  transfer,  namely:     Radiation,  Con- 
duction, and  Convection. 

69.  Radiation.  —  Radiation  is  the  transmission  of  heat  through 
an  intervening  space  in  the  same  manner  that  light  is  trans- 
mitted.    We  sometimes  speak  of  feeling  the  "glow"  from  a  fire 
when  at  some  distance  from  it.     This  glow  is  really  the  radiant 
heat  from  the  fire.     That  part  of  a  boiler  shell  which  is  directly 
over  the  fire  receives  the  radiant  heat  from  the  fire  and,  as  this 
heat  is  very  intense  at  such  a  short  distance,  the  shell  heating 
surface  is  very  effective  in  raising  steam. 

70.  Conduction.  —  When  a  silver  spoon  is  placed  in  a  cup  of 
hot  tea  or  coffee  the  handle  soon  becomes  warm.     The  bowl  of 
the  spoon  receives  the  heat  and  transmits  it  to  the  hand  by  a 
process  which  we  call  conduction.     According  to  our  theory  of 
heat,  conduction  must  consist  simply  in  the  transfer  of  motion 
from   one   molecule  to   the   next.     Some   metals,   we   find   by 
experience,  will  conduct  heat  faster  than  others.     Silver  is  the 
best  conductor  and  copper  is  almost  as  good,  while  brass  will 
only  transmit  heat  at  about  one-fourth  the  rate  of  silver  and,  even 
then,  it  is  nearly  twice  as  good  a  conductor  of  heat  as  iron.     The 
following  table  gives  the  relative  conductivities  of  some  common 
substances,  that  of  silver  being  taken  as  100.     It  will  be  noticed 
that  even  though  there  is  a  wide  difference  in  the  conductivities 
of  the  metals  they  are  all  greater  than  those  of  other  substances. 

RELATIVE  HEAT  CONDUCTIVITIES 


Silver  

100 

Lead 

8.5 

Copper  

90 

Glass          

.15 

Aluminum     .  .    . 

50 

Wood                     .... 

.01 

Brass 

25 

Magnesia 

.007 

Steel  and  Iron  

15 

Asbestos  

.007 

92  STEAM  BOILERS 

The  low  values  for  magnesia  and  asbestos  explain  why  these  and 
similar  substances  are  used  for  pipe  coverings. 

When  the  hot  gases  from  a  boiler  furnace  come  in  contact  with 
the  shell  and  the  tubes,  some  of  the  heat  of  the  gases  is  trans- 
ferred to  the  metal.  The  transfer  is  made  by  conduction,  the 
molecules  of  the  gases  transferring  some  of  their  energy  to  the 
molecules  of  iron  on  the  surface  of  the  metal.  This  heat  is 
next  transmitted  through  the  shell  from  the  outer  to  the  inner 
surface  by  conduction  and  is  then  given  to  the  water  lying  on  the 
inside  by  the  same  process.  The  radiant  heat  received  by  the 
metal  directly  from  the  fire  is  likewise  transmitted  through  the 
metal  to  the  water  by  conduction. 

From  the  table  of  conductivities  it  would  appear  as  if  there 
were  several  metals  better  suited  for  boiler  construction  than 
iron  or  steel.  Iron  and  steel  are,  as  we  know,  both  cheap  and 
strong  and  we  find  in  practice  that  these  conductivities  are  not 
so  important  as  they  seem.  The  tubes  and  plates  of  a  boiler 
are  comparatively  thin  and  the  difference  in  temperature  between 
the  outside  and  inside  is  so  great  that  the  kind  of  metal  does  not 
make  a  great  deal  of  difference.  Their  importance  is  also  reduced 
by  the  fact  that  thinner  plates  of  steel  can  be  used  than  of  other 
metals  because  of  its  greater  strength.  There  is  undoubtedly 
some  difference,  however,  and  we  find  brass  and  copper  tubes 
used  in  many  fire-engine  boilers  and  in  large  numbers  of  European 
locomotives. 

71.  Convection. — Liquids  and  gases  are  very  poor  conductors, 
but  they  have  another  method  of  transferring  heat  that  is  very 
effective.  Fill  a  bottle  or  a  test-tube  with  water  and,  grasping 
it  near  the  bottom,  hold  the  upper  end  in  a  gas  flame  as  illus- 
trated in  Fig.  61.  The  water  will  soon  boil  at  the  surface  but  the 
lower  end  of  the  bottle  will  remain  quite  cool.  It  will  be  evident 
from  this  that  water  is  a  poor  conductor  of  heat. 

Again  filling  the  tube,  hold  it  by  the  top  and  apply  the  flame 
to  the  base  as  in  Fig.  62.  As  fast  as  the  water  receives  heat  at 
the  bottom  it  will  rise  to  the  top  and  the  upper  end  of  the  tube 
will  be  practically  as  hot  as  the  bottom.  The  heat  in  this  case 
is  transferred  from  one  end  of  the  tube  to  the  other  by  a  current 
in  the  water,  and  this  method  of  transferring  heat  is  called 
convection. 

In  boiler  operation  the  movement  of  water  from  one  part  of 
the  boiler  to  another,  caused  by  heat,  is  spoken  of  as  circulation. 


EFFECTS  OF  HEAT 


93 


The  water  lying  next  to  the  heating  surface  of  a  boiler  receives 
heat  from  the  metal.  This  water  expands  as  it  becomes  warmer 
and  therefore  rises,  while  the  cooler  water,  being  denser,  descends 
to  the  bottom.  By  the  circulation  thus  set  up,  the  heat  is  dis- 
tributed throughout  the  entire  body  of  water  and,  if  the  circula- 
tion is  rapid,  the  entire  contents  of  the  boiler  will  be  at  the  same 
temperature. 


FIG.  61. 


FIG.  62. 


72.  Circulation. — The  circulation  in  a  boiler  is  a  most  important 
item  and  should  be  facilitated  as  much  as  possible.  The  capacity 
of  a  boiler  depends  largely  upon  the  character  of  the  circulation. 
The  metal  parts  of  the  boiler,  such  as  the  shell  and  tubes,  will 
transmit  heat  very  fast,  much  faster,  in  fact,  than  is  generally 
supposed  and,  in  order  to  take  advantage  of  this  ability  to 
transmit  heat  rapidly,  it  is  necessary  to  have  water  sweeping 
over  the  metal  with  a  strong  rapid  movement  so  as  to  keep  the 
steam  bubbles  swept  from  the  surface.  Steam  is  an  even  poorer 
conductor  of  heat  than  water,  and,  if  allowed  to  collect  in  pockets 
next  to  metal  which  is  transmitting  a  large  quantity  of  heat,  the 
steam  will  be  unable  to  conduct  the  heat  away  fast  enough  and 
the  metal  will  be  overheated  and  burned.  It  has  been  found  by 
experiment  that  as  long  as  water  flows  freely  along  a  boiler  tube 
it  is  impossible  to  burn  the  tube,  even  with  the  most  intense  heat, 
but  if  steam  is  allowed  to  remain  in  contact  with  the  surface,  it 
may  be  melted  quickly. 

Overheating  of  the  metal  in  spots  will  also  cause  unequal 
expansion  in  different  parts  of  the  boiler,  and  the  strains  thus 


94  STEAM  BOILERS 

set  up  may  cause  serious  damage.  A  boiler  having  a  rapid 
circulation  will  respond  quicker  to  changes  in  load,  and  steam 
may  be  raised  more  readily  than  in  one  in  which  the  circula- 
tion is  poor. 

A  rapid  circulation  also  serves  to  sweep  away  any  films  of 
air  that  may  separate  from  the  water  and  collect  on  the  surface. 
Air  which  separates  from  water  in  a  boiler  is  very  injurious  as 
it  causes  rapid  corrosion.  In  the  same  way,  rapid  circulation 
prevents  the  accumulating  of  grease  and  oil  on  the  heating 
surface;  this  is  especially  true  where  the  water  sweeps  rapidly 
over  the  surface  as  in  a  small  tube  of  a  water-tube  boiler. 
By  reason  of  the  cleansing  action  of  a  rapid  current  of  water, 
deposits  of  mud  and  sediment  are  not  likely  to  settle  as  thickly 
in  the  tubes  of  water-tube  boilers  as  in  those  portions  where 
the  current  is  less  rapid. 

The  circulation  in  a  boiler  depends  largely  upon  the  form  of 
the  heating  surface  and,  as  circulation  is  so  important,  a  great 
deal  of  attention  is  given  in  designing  boilers,  to  have  them  of 
such  shape  as  to  aid  the  circulation.  In  a  return  fire-tube  boiler 
the  water  will  rise  in  the  front  end  over  the  furnace,  move  toward 
the  back  end  near  the  surface  of  the  water  and  will  then  pass  to 
the  bottom  near  the  rear  end  and  along  the  bottom  toward  the 
front.  Of  course  all  the  water  does  not  follow  this  path,  as 
some  of  it  is  rising  from  all  parts  of  the  tubes  and  all  along  the 
bottom  of  the  shell.  In  water-tube  boilers  the  direction  of  the 
circulation  will  depend  largely  on  the  position  of  the  tubes.  In 
inclined  water-tube  boilers,  such  as  the  B.  &  W.,  the  circulation 
is  from  rear  to  front  through  the  tubes,  then  up  the  front  header 
to  the  steam  drum,  through  the  steam  drum  to  the  rear  header 
and  down  the  rear  header  to  the  tubes. 

In  order  to  aid  circulation  and  avoid  bringing  cold  water  in 
contact  with  heated  surfaces  of  the  boiler,  the  feed  water  should 
be  discharged  into  the  boiler  only  after  it  has  become  heated, 
and  even  then  it  should  be  discharged  in  the  same  direction  as 
the  circulation.  In  a  return  fire-tube  boiler  this  result  can  best 
be  secured  by  introducing  the  feed  pipe  through  the  front  head 
a  few  inches  below  the  surface  of  the  water  and  near  one  side. 
The  pipe  should  then  pass  straight  back  to  within  a  few  inches 
of  the  rear  head,  then  across  the  boiler  to  the  other  side  and 
discharge  downward  among  the  tubes.  The  pipe  may  be  per- 
forated where  it  passes  across  at  the  back  but  the  perforations 


EFFECTS  OF  HEAT 


95 


should  discharge  toward  the  rear  head  or  downward.  Introduc- 
ing the  feed  water  in  this  way  will  allow  it  to  become  heated  in 
the  feed  pipe  before  it  is  discharged  against  any  hot  surfaces. 
In  no  case  should  a  feed  pipe  end  as  soon  as  it  enters  the  shell, 
unless  the  water  is  pumped  into  the  boiler  by  means  of  an  injector, 
which  will  heat  it  to  about  the  same  temperature  as  exists  in 
the  boiler. 

73.  Formation  of  Steam. — Since  heat  is  necessary  to  effect 
the  transformation  of  water  into  steam,  it  follows  that  the  steam 
will  be  formed  from  water  in  immediate  contact  with  the  heating 
surface  of  a  boiler.  In  the  hottest  parts  of  the  boiler  we  there- 
fore have  a  mixture  of  hot  water  and  bubbles  of  steam.  As 
these  bubbles  occupy  a  much  larger  volume  than  the  water  from 


FIG.  63. 


FIG.  64. 


which  they  were  formed,  they  are  lighter  and  tend  to  rise  to  the 
surface  with  the  heated  water.  Each  bubble  of  steam  is  under  a 
pressure  equal  to  that  on  the  surface  of  the  water  plus  the  weight 
of  the  water  above  the  bubble.  As  it  rises  toward  the  surface 
the  pressure  becomes  less  and  the  steam  inside  the  bubble  ex- 
pands. At  the  same  time,  the  velocity  with  which  it  is  rising 
increases  as  it  approaches  the  surface  and  when  the  bubble  reaches 
the  surface  it  bursts  the  film  of  water  which  encloses  it.  The 
finely  divided  particles  of  water  are  thrown  up  into  the  steam 
above  the  water  and,  as  these  particles  of  water  are  very  small, 
they  remain  suspended  in  the  steam  just  as  moisture  remains 
suspended  in  air  during  a  fog.  This  water  is  not  in  the  form  of 
steam  but  is  merely  water  in  mechanical  suspension.  This  causes 


96  STEAM  BOILERS 

the  steam  to  be  wet  or  moist.  When  a  boiler  delivers  wet  steam 
into  the  steam  pipes  it  is  said  to  prime.  It  can  be  readily  seen 
that  the  faster  steam  is  formed  or  the  more  the  boiler  is  forced, 
the  greater  will  be  the  priming.  The  character  of  the  circulation 
greatly  affects  the  tendency  to  prime.  A  boiler  having  a  strong 
positive  circulation  can  be  forced  much  harder  without  priming 
than  can  one  with  a  poor  circulation.  This  can  be  readily 
appreciated  by  reference  to  Figs.  63  and  64.  If  water  is  boiled 
in  a  vertical  tube  as  in  Fig.  63,  the  steam  will  form  at  the  bottom 
of  the  tube  in  large  bubbles.  The  rising  steam  opposes  the  down- 
ward passage  of  the  water  and  if  the  heat  is  intense  the  entire 
contents  of  the  tube  may  be  thrown  out  with  almost  explosive 
violence.  Now  observe  how  smoothly  and  positively  the  circula- 
tion would  occur  in  a  system  such  as  shown  in  Fig.  64,  and  there- 
fore how  much  faster  the  evaporation  could  occur  without  any 
excessive  priming  action. 

74.  Disengagement  Surface. — The  Disengagement  Surface  or 
Disengagement  Area  refers  to  the  surface  of  the  water  from  which 
the  steam  escapes  into  the  steam  space  above.     It  is  important 
that  this  area  should  be  large,  especially  in  flue  or  fire-tube 
boilers  where  there  is  not  a  positively  denned  circulation.     If 
too  much  steam  escapes  from  a  small  area,  it  will  keep  the  surface 
of  the  water  in  violent  agitation  and  cause  priming  and  may 
even  cause  the  water  gage  to  indicate  a  false  water  level. 

75.  Steam  Space. — The  amount  of  steam  space  in  a  boiler 
also  affects  the  possibility  of  priming.     If  the  steam  space  is  too 
small  the  steam  will  be  drawn  off  before  it  has  time  to  deposit 
its  moisture.     With  an  ample  steam  space  the  moisture  thrown 
up  will  have  an  opportunity  to  settle  back  upon  the  surface  of  the 
water  before  it  enters  the  steam  main.     This  explains  the  reason 
for  placing  domes  on  many  fire-tube  boilers.     For  instance,  in  a 
locomotive,  where  the  formation  of  steam  is  very  rapid,  the  main 
steam  pipe  is  taken  from  the  top  of  the  dome  in  order  to  have  the 
entrance  of  the  pipe  as  far  removed  from  the  surface  of  the  water 
as  possible.     When  a  dome  is  not  provided,  the  moisture  is 
separated  from  the  steam  by  either  a  dry  pipe  or  by  a  baffle  plate 
which  prevents  the  moisture  from  being  carried  into  the  steam 
line. 


CHAPTER  VII 
PROPERTIES  OF  STEAM 

76.  Atmospheric  Pressure. — The  atmosphere  which  surrounds 
the  earth  exerts  a  pressure  on  all  bodies  on  the  earth's  surface. 
Air  has  weight  and,  since  it  extends  upward  from  the  earth's 
surface  a  distance  usually  estimated  at  about  50  miles,  the  weight 
of  this  air  presses  on  any  object  on  the  earth's  surface. 

At  the  level  of  the  ocean  (or  "sea  level,"  as  it  is  called)  the 
pressure  of  the  atmosphere  averages  14.7  Ib.  on  each  square  inch 
of  surface,  although  it  varies  according  to  the  weather.  Moist 
air  is  lighter  than  dry  air;  therefore,  the  atmospheric  pressure 
will  be  less  on  a  damp  day  than  on  a  dry  one. 

In  other  parts  of  the  country  the  atmospheric  pressure  is  less 
than  at  sea  level,  because,  being  above  sea  level,  the  column  of 
air  which  produces  the  pressure  is  not  so  high.  The  decrease  in 
pressure  is  about  1/2  Ib.  for  each  1000  ft.  above  sea  level.  This 
figure  is  usually  sufficiently  accurate  up  to  2  miles  above  sea  level, 
but,  since  the  air  gradually  becomes  rarer  as  we  go  upward,  the 
pressure  decreases  less  rapidly  at  high  altitudes.  Since  the  actual 
atmospheric  pressure  depends  upon  weather  conditions  as  well 
as  upon  altitude,  the  only  reliable  method  of  ascertaining  the 
pressure  at  a  particular  time  and  place  is  to  measure  it  with 
a  barometer. 

77.  Barometers. — A  barometer  is  a  device  for  measuring  the 
pressure  of  the  atmosphere.     The  simplest  form  of  barometer 
is  made  as  follows:     Take  a  glass  tube  about  3  ft.  long  having 
one  end  sealed,  and  completely  fill  it  with  mercury.     Place  the 
finger  over  the  open  end  and  invert  the  tube.     Place  the  open 
end,  still  covered  with  the  finger,  in    a  cup  of   mercury  and 
then  remove  the  finger.     The  mercury  in  the  tube  will  descend 
until  it  stands  at  a  height  h,  Fig.  65,  which  indicates  the  atmos- 
pheric pressure.     The  atmosphere  presses  on  the  surface  of  the 
mercury  in  the  cup,  but  there  is  no  pressure  on  the  surface  of  the 
mercury  in  the  tube.     Therefore,  the  mercury  in  the  tube  must 
stand  at  such  a  height  that  the  pressure  at  the  bottom  of  the 
column  will  balance  the  pressure  of  the  atmosphere. 

One  cubic  inch  of  mercury  weighs  .4908  lb.;  and,  therefore, 
10  97 


98 


STEAM  BOILERS 


FIG 


each  inch  of  mercury  in 'the  tube  above  the  level  in  the  cup 
will  represent  an  atmospheric  pressure  of  .4908  Ib.  per  square 
inch.  At  sea  level  we  find  a  mercury  barometer  will 
usually  stand  at  30  in.,  indicating  a  pressure  of 


30  X.  4908  =  14.724  Ib.  per  square  inch. 

The  commonly  used  figure  14.7,  corresponds  to  29.92 
in.  or  an  elevation  of  69  ft.  above  sea  level.  Although 
30  in.  and  14.7  Ib.  do  not  exactly  agree,  they  are 
both  used  as  representing  the  pressure  at  sea  level. 
Barometers  are  made  in  other  ways  than  by  the  use 
of  mercury,  but  they  are  usually  graduated  so  as  to 
read  in  "  inches  of  mercury."  If  water  were  used 
instead  of  mercury,  it  would  require  a  tube  over  34 
ft.  long,  since  water  weighs  .036  Ib.  per  cubic  inch. 

78.  Gage  Pressures.  —  The  ordinary  steam  gage  used 
on  boilers  indicates  the  difference  between  the  steam 
pressure  within  the  boiler  and  that  of  the  atmosphere 
on  the  outside.  The  steam  exerts  a  certain  pressure 
outward  against  the  walls  of  the  boiler  and  the  atmos- 
phere exerts  a  certain  pressure  inward  against  the 
walls.  Owing  to  the  construction  of  the  steam  gage,  it  indicates 
the  amount  by  which  the  steam  pressure  inside  the  boiler  is 
greater  than  the  atmospheric  pressure  on  the  outside.  This  is 
called  Gage  Pressure. 

79.  Absolute  Pressure.  —  The  true  way  to  measure  pressure  is 
from  an  entire  absence  of  pressure  (or  absolute  zero  pressure). 
The  absolute  pressure  in  a  boiler  is  the  sum  of  the  pressure 
indicated  by  the  gage  and  the  pressure  of  the  atmosphere  as 
indicated  by  the  barometer.  In  the  absence  of  any  barometer, 
we  generally  assume  that  14.7  Ib.  per  square  inch  is  the  atmos- 
pheric pressure  and  add  this  to  the  pressure  indicated  by  the 
gage,  unless  we  have  some  more  definite  idea  as  to  the  average 
barometric  pressure  in  our  locality.  For  example,  suppose  the 
steam  gage  on  a  boiler  reads  120  Ib.  The  absolute  pressure  in 
the  boiler  will  be  120  +  14.7  =  134.7  Ib.  per  square  inch,  if  we 
consider  the  atmospheric  pressure  as  being  14.7  Ib.  per  square 
inch.  Suppose  we  knew  that  a  barometer  at  this  locality  read 
28.5  in.,  the  absolute  pressure  would  then  be  120  +  (.4908  X 
28.5)  =120  +  13.99  =  133.99  Ib.  per  square  inch. 

80.  Vacuum.  —  A  vacuum  is  a  space  from  which  all  matter 


PROPERTIES  OF  STEAM 


99 


(including  the  air)  is  removed  and,  therefore,  is  indicated  by  a 
zero  absolute  pressure.  If  we  have  a  cylinder  of  air  at  atmos- 
pheric pressure  and  then  pump  out  part  of  the  air  so  that  the 
pressure  is  less  than  that  of  the  surrounding  atmosphere,  we 
have  in  the  cylinder  a  partial  vacuum.  If  we  were  able  to  remove 
all  of  the  air,  we  would  then  have  a  total  or  absolute  vacuum. 
The  chief  use  of  vacuums  in  power-plant  work  is  in  condensers. 
By  cooling  and  thus  condensing  the  exhaust  steam  from  an 


FIG.  66. 

engine,  the  change  in  volume  when  the  steam  is  turned  to  water 
is  so  great  that  a  high  vacuum  is  obtained  in  the  exhaust  pipe 
and  the  condenser. 

Vacuums  are  usually  measured  by  the  reduction  of  the  pressure 
below  that  of  the  surrounding  atmosphere.  If  the  top  of  the 
glass  tube  in  Fig.  65  were  opened  to  the  atmosphere,  the  mercury 
would  immediately  drop  to  the  level  of  that  in  the  cup,  because 
the  pressure  on  the  mercury  in  the  tube  would  then  be  the  same 
as  that  on  the  mercury  in  the  cup.  If  now  we  were  to  connect 
the  top  of  the  tube  with  a  suction  pump,  as  in  Fig.  66,  arid  ciraw 


100 


STEAM  BOILERS 


out  the  air,  the  difference  in  pressure  would  cause  the  mercury 
to  rise  in  the  tube.  The  more  we  pumped,  the  higher  would  the 
mercury  rise,  and  the  height  of  the  mercury  would  indicate  the 
difference  in  pressure  between  the  atmosphere  and  the  pump 
cylinder.  As  previously  explained,  this  can  be  reduced  to 
pounds  per  square  inch  by  multiplying  the  inches  of  mercury 
by  .4908.  Vacuum  gages  do  not  always  make  use  of  the  mercury 

column,  but  nevertheless  are  nearly 
always  graduated  to  read  in  "  inches 
of  mercury  below  atmosphere."  The 
absolute  pressure  corresponding  to  a 
certain  vacuum  can  be  obtained  by 
finding  the  difference  between  the  read- 
ing of  the  barometer  and  the  reading 
of  the  vacuum  gage.  To  illustrate  this, 
suppose  the  vacuum  gage  on  a  con- 
denser indicates  24  in.  of  vacuum  on  a 
day  when  the  barometer  reads  28.5  in. 
The  difference  between  the  atmos- 
pheric pressure  and  the  pressure  in 
the  condenser  is 


25- 


20- 


15- 


5- 


Atmospheric 
pressure 


14.7- 


—50 


-45 


-40 


-30 


-25 


-20 


•  V) 

Li     I 


-5 


28.5-24  =  4.5  in. 
4.5  X  .4908  -  2.21  Ib.  per  sq.  in. 

Because  of  the  difference  in  atmos- 
pheric  pressures  at  different  altitudes, 
a  vacuum  that  is  readily  obtained  in 
some  places  is  very  difficult  or  impossi- 
ble  to  obtain  in  other  places.  At  sea 
level  a  vacuum  of  28  in.  is  readily  main- 
tained in  condensers  because  the  at- 
mospheric pressure  is  about  30  in., 
which  would  leave  an  absolute  pressure 
of  2  in.  of  mercury  or  .98  Ib.  per  square  inch.  On  the  other  hand, 
this  same  vacuum  is  unattainable  in  some  of  the  western  cities 
because  the  altitude  is  such  that  even  the  barometer  does  not  stand 
this  high.  If  the  barometer  stands  at  only  26  in.,  a  vacuum  gage 
in  order  to  have  the,same  absolute  pressure  of  2  in.  would  record 
onlv  24  in.  of  vacuum.  Remember  that  the  barometer  and  vacuum 
gage  read  in  opposite  directions,  the  barometer  indicating  the  ab- 
solute pressure  of  the  atmosphere  while  the  vacuum  gage  indi- 
cates the  reduction  in  pressure  below  that  of  the  atmosphere. 


FIG.  67. 


PROPERTIES  OF  STEAM  V/A:fy^ 

Fig.  67  shows  the  relation  between  absolute  pressure,  gage 
pressure,  and  vacuum,  all  expressed  in  pounds,  with  an  atmos- 
pheric pressure  •  of  14.7  Ib.  per  square  inch.  If  the  atmos- 
pheric pressure  were  14  Ib.  per  square  inch  the  gage  pressure  and 
vacuum  scales  would  be  lowered  so  that  their  zero  reading  would 
be  opposite  14  Ib.  absolute. 

81.  Evaporation. — If  we  take  an  ordinary  tea-kettle  or  pan 
containing  water  and  place  it  over  a  fire  we  will  observe  the 
following  changes :  At  first  the  water  will  merely  rise  in  tempera- 
ture, but  after  it  has  reached  a  temperature  somewhere  near  212° 
F.  boiling  begins  and  steam  is  given  oft7.  If  we  continue  to 
apply  heat  after  the  boiling-point  is  reached  we  notice  that  the 
temperature  remains  stationary.  If  less  heat  is  applied  the 
water  boils  slowly  and  if  more  heat  is  added  the  water  boils 
faster;  but  in  either  case  the  temperature  remains  constant  until 
all  the  water  is  evaporated. 

If  the  water  is  boiled  in  a  closed  vessel  under  a  pressure  above 
that  of  the  atmosphere,  a  higher  temperature  than  212°  F.  is 
necessary  to  start  boiling.  On  the  other  hand,  if  a  pressure  less 
than  atmospheric  is  maintained  in  the  vessel  by  means  of  a 
vacuum  pump  or  otherwise,  the  water  boils  at  a  much  lower 
temperature.  Experiments  show  also  that  the  amount  of  heat 
required  to  change  the  water  to  steam  after  the  boiling  tem- 
perature is  reached  is  different  for  different  pressures. 

It  is  thus  seen  that  for  each  pressure  at  which  the  steam  is 
formed  there  is  a  definite  corresponding  temperature  at  which 
evaporation  occurs.  If  the  pressure  is  great  the  corresponding 
temperature  is  high  and  if  the  pressure  is  low  the  temperature  is 
low.  The  temperature  of  steam  formed  at  a  certain  pressure 
may  be  further  increased  without  increasing  its  pressure  if  it  is 
taken  away  from  the  presence  of  water  and  heated;  but  an  at- 
tempt to  increase  the  temperature  of  steam  while  it  is  in  contact 
with  water  results  only  in  boiling  the  water  faster  and  forming 
more  steam.  If  an  attempt  is  made  to  lower  the  temperature  of 
the  steam,  a  portion  of  it  will  be  condensed. 

In  order  to  make  boiler  tests  or  to  study  in  any  other  way 
the  operation  of  a  boiler,  it  is  necessary  to  know  the  exact  amount 
of  heat  used  in  generating  each  pound  of  steam.  In  calculating 
the  size  of  a  steam  line,  it  is  desirable  to  know  just  how  much 
space  is  occupied  by  1  Ib.  of  steam  and  how  much  a  cubic  foot  of 
steam  weighs.  All  such  quantities  are  called  "Properties  of 


J.02  STEAM  BOILERS 

Steam."  These  have  been  observed  and  recorded  for  our  use  by 
various  scientists,  and  the  results  of  their  observations  have 
been  arranged  in  tables  which  we  call,  for  short,  Steam  Tables. 
Numerous  formulas  have  been  devised  that  will  give  more  or 
less  accurately  the  different  properties,  but  it  is  much  easier  and 
more  accurate  to  use  the  tables.  With  this  chapter  is  included  a 
Steam  Table  for  the  use  of  the  student  in  this  course  and  in  his 
future  work.  The  values  given  in  the  tables  are  for  1  Ib.  of  water  or 
steam. 

82.  Saturated  Steam. — It  will  be  noticed  that  the  table  is 
headed.  " Properties  of  Saturated  Steam"  and  the"  question 
naturally  arises,  "What  is  meant  by  saturated  steam?"  By 
saturated  steam  we  mean  steam  that  is  at  the  evaporation 
temperature  corresponding  to  its  pressure.  As  steam  is  formed 
in  a  boiler  and  rises  from  the  surface  of  the  water,  it  is  saturated 
and  will  remain  so  as  long  as  it  is  in  contact  with  water.  So 
long  as  the  steam  is  in  a  boiler  or  in  close  communication  with 
water,  it  cannot  be  other  than  saturated.  Any  attempt  to  heat 
the  steam  higher  will  fail,  as  it  will  merely  transmit  the  heat  to 
the  water  and  cause  further  evaporation.  To  effect  superheat, 
the  steam  must  be  removed  from  close  communication  with 
water.  Steam  is  superheated  by  heating  it,  away  from  water,  to  a 
higher  temperature  than  its  boiling-point,  without  changing  the 
pressure. 

Saturated  steam  may  be  "dry ".or  "wet."  Dry  steam  is  as 
clear  and  transparent  as  air  and  is  not  visible  to  the  eye.  The 
steam  which  we  see  in  the  exhaust  from  an  engine  is  wet  steam  and 
the  visible  part  consists  of  particles  of  water,  or  condensed  steam. 

Do  not  get  the  idea  that  saturated  steam  necessarily  means  wet 
steam.  Saturated  steam  may  be  perfectly  dry.  One  may  show 
this  clearly  by  taking  a  small  glass  bottle,  partially  filling  it 
with  water,  and  placing  it  loosely  corked  on  the  stove.  When 
the  water  boils,  no  mist  is  seen,  such  as  we  usually  imagine  to  be 
the  appearance  of  steam.  The  bottle  will  remain  perfectly 
transparent  just  as  if  filled  with  air.  The  exhaust  from  an 
engine  is  visible  only  because  of  the  water  which  it  contains. 
This  water  is  divided  into  fine  particles  and  is  suspended  in  the 
steam  just  as  water  is  suspended  in  the  air  during  a  fog.  When 
a  boiler  is  blown  off,  or  when  a  whistle  is  blown,  it  will  be  noticed 
that  steam  is  not  visible  until  it  is  about  3  or  4  in.  from  the  end  of 
the  pipe,  where  some  of  it  has  been  condensed  by  the  colder  air. 


PROPERTIES  OF  STEAM  103 

Whenever  steam  is  mentioned  saturated  steam  is  meant.  If  the 
steam  is  superheated  it  is  spoken  of  as  superheated  steam. 

83.  Steam  Tables. — The  steam  tables  should  be  studied  very 
carefully,  as  any  one  working  problems  relating  to  steam  will  be 
using  them  constantly,  and  it  requires  considerable  study  to 
become  proficient  in  their  use. 

All  steam  tables  are  made  out  for  1  Ib.  weight  of  steam  and 
the  quantities  given  in  them,  such  as  the  Heat  of  the  Liquid, 
Latent  Heat  of  Evaporation,  Specific  Volume,  etc.,  are  the 
quantities  of  heat  or  volume  of  1  Ib.  weight  of  dry  steam  (the  steam 
formed  from  1  Ib.  of  water).  To  find  these  quantities  for  a  given 
weight  of  steam,  it  is  necessary  to  multiply  the  figures  given  in 
the  steam  table  by  the  weight  of  the  steam  in  pounds.  The 
column  giving  the  density  or  weight  per  cubic  foot  of  steam  is, 
of  course,  an  exception  to  the  statement  that  the  tables  give  only 
values  for  1  Ib.  of  steam. 

84.  Pressures. — The  properties  of  steam  depend  on  the  abso- 
lute pressure  to  which  the  steam  is  subjected.     The  pressure  of- 
fers a  certain  resistance  to  the  expansion  of  the  water  into  steam, 
and  it  is  the  amount  of  this  resistance  that  determines  the  tem- 
perature of  evaporation  and  the  other  quantities.     Consequently, 
the  absolute  pressure  is  the  first  item  to  be  given  in  the  tables. 

For  convenience,  the  corresponding  gage  pressures  are  given 
in  the  second  column,  assuming  an  atmospheric  pressure  of  14.7 
Ib.  per  square  inch.  In  case  the  barometer  shows  an  atmospheric 
pressure  very  different  from  this,  it  is  best  to  add  the  barometer 
and  gage  pressures  and  thus  get  the  absolute  pressure,  which 
should  then  be  used  for  finding  the  properties  of  the  steam.  In 
using  properties  of  steam  at  pressures  below  atmospheric,  it  is 
especially  desirable  to  calculate  the  absolute  pressure  from  barom- 
eter and  vacuum  gage  readings  rather  than  to  use  the  vacuum 
reading  in  the  gage  pressure  column  of  the  table.  An  example 
will  show  readily  what  a  difference  this  may  make. 

Suppose  a  vacuum  gage  on  a  condenser  shows  a  vacuum  of 
27  in.  and  we  want  to  find  the  temperature  at  which  the  steam  is 
condensing.  Without  knowing  the  barometer  reading  we  would 
say  that 

27X. 4908  =  13.25  + 

and  that  at  a  vacuum  of  13.25  Ib.  (  -13.25  Ib.  gage),  which  corre- 
sponds to  an  absolute  pressure  of  1.45  Ib.  per  sq.  in.,  water 
boils  or  condenses  at  a  little  less  than  115.9°  F.,  say  about  115°. 
This  assumes  that  the  barometer  reading  is  29.92  in. 


104  STEAM  BOILERS 

Now,  suppose  that  we  first  look  at  a  barometer  and  find  that  it 
stands  at  only  28  in.  Our  condenser  has  more  of  a  vacuum  than 
we  thought  it  had.  The  absolute  pressure  in  the  condenser  is 

(28  -27)  X  .4908  =  .4908  Ib.  per  sq.  in. 

or  not  quite  .5  Ib.  per  sq.  in.  absolute,  and  we  find  that  the 
temperature  of  the  steam  and  water  in  the  condenser  is  a  little 
less  than  79°  F.,  instead  of  being  115°. 

85.  Temperature  of  Evaporation.  —  The  third  column  in  the 
table  gives  the  temperatures  at  which  water  evaporates  when 
under  the  pressures  given  in  the  first  and  second  columns.  These 
temperatures  are  also  the  temperatures  of  saturated  steam  at  the 
given  pressures  and  are  likewise  the  temperatures  at  which  steam 
under  the  given  pressures  will  condense. 

When  water  is  heated  in  an  open  vessel  under  atmospheric 
pressure  (14.7  Ib.  absolute),  it  boils  at  212°  F.  If  the  pressure 
is  reduced,  the  resistance  to  the  formation  of  steam  is  diminished 
and  evaporation  takes  place  at  a  lower  temperature.  For  exam- 
ple, in  a  vacuum  of  28  in.  (.943  Ib.  absolute  pressure)  water  will 
boil  at  100°  F.  and  if  the  absolute  pressure  is  reduced  to  .089  Ib., 
water  will  evaporate  at  32°  F.  On  the  other  hand,  if  water  is 
under  a  pressure  greater  than  that  of  the  atmosphere,  it  will 
require  a  temperature  higher  than  212°  F.  to  cause  it  to  boil. 
This  is  the  condition  which  usually  exists  in  the  common  steam 
boiler.  If  the  absolute  pressure  in  a  boiler  is  144  Ib.  (129.3  Ib. 
gage),  the  temperature  of  both  the  water  and  the  steam  in  the 
boiler  is  355°  F.  A  thermometer  placed  in  a  boiler  would  serve 
as  a  pressure  gage  .but  perhaps  would  not  be  as  convenient  for 
the  fireman. 

Formulas  have  been  worked  out  by  which  we  can  get  the  boil- 
ing temperature  for  a  certain  pressure,  or  vice  versa.  One  of  the 
simplest  of  these  is: 

2900 
=  ~ 


and  in  which   t  is  the   temperature   of  the  steam  in  degrees 
Fahrenheit,  and  log  P  is  the  logarithm  of  the  absolute  pressure. 

Example  :  What  is  the  temperature  of  steam  having  an  absolute 
pressure  of  100  Ib.  per  sq.  in.? 

The  logarithm  of  100  is  2. 


PROPERTIES  OF  STEAM  105 

which  is  within  0.2  degrees  of  the  temperature  given  in  the  steam 
table. 

However,  it  would  be  necessary  to  consult  a  table  of  logarithms 
in  order  to  make  use  of  this  formula,  and,  since  steam  tables  are 
just  as  easily  consulted  as  logarithm  tables,  this  formula  is  of 
little  practical  use. 

The  absolute  pressure  in  pounds  per  square  inch  may  be  found 
approximately  from  the  following  formula: 

I+IOO 


62.66 

in  which  t  is  the  temperature  of  the  steam  in  degrees  Fahrenheit. 
Example  :  What  will  be  the  pressure  of  steam  having  a  tem- 
perature of  300°? 

300+  100  V 


4«        4096 

62.66        "  62.66"  62.66" 
while  the  steam  table  gives  67.2  Ib. 

This  is  not  a  very  accurate  way  to  find  the  pressure  but  the 
method  of  calculating  it  accurately  is  very  complicated.  This 
formula  gives  results  which  do  not  vary  more  than  21/2  Ib.  from 
the  values  given  in  the  steam  table,  and  at  pressures  near  that 
of  the  atmosphere,  the  results  given  by  the  formula  do  not  vary 
more  than  0.1  Ib.  from  those  given  in  the  table. 

86.  Heat  of  the  Liquid.  —  In  the  formation  of  steam,  the  water 
must  first  be  raised  to  the  boiling  temperature.  The  heat  it 
then  contains,  measured  from  32°  F.,  is  called  the  Heat  of  the 
Liquid.  In  other  words,  the  heat  of  the  liquid  is  the  amount 
of  heat  which  is  required  to  raise  the  temperature  of  1  Ib.  of  the 
water  from  32°  F.  to  the  boiling-point.  Approximately,  the  value 
of  the  heat  of  the  liquid  per  pound  is  the  difference  between  the 
boiling  temperature  and  32°  F.,  since  the  specific  heat  of  water  is 
about  1.  Written  as  a  formula: 

h  =  t-32 

in  which  h  is  the  heat  of  the  liquid,  and  t  is  the  boiling  temperature 
of  the  water.  For  rough  calculations  this  is  close  enough,  but 
for  accurate  work,  steam  tables  should  be  used  since  the  specific 
heat  of  water  is  not  exactly  1  at  all  temperatures,  but  varies 
slightly. 

At   atmospheric   pressure  the  temperature  of  evaporation  is 


106  STEAM  BOILERS 

212°  F.  Obtaining  the  heat  of  the  liquid  by  difference  in  tem- 
peratures, h  =  2 12  —32  =  180  B.t.u.  If  we  refer  to  steam  tables, 
we  find  the  exact  value  to  be  180.8  B.t.u.  or  an  increase  of  0.45 
per  cent  over  the  first  number.  At  165  Ib.  absolute  (150.3  Ib. 
gage),  the  evaporation  temperature  is  365.9°  F.  This  would  give 
by  difference  in  temperatures  a  value  of  365.9  —32=333.9  B.t.u. 
for  the  heat  of  the  liquid,  while  the  actual  value  is  332.4  B.t.u., 
an  increase  of  over  1  per  cent.  Whenever  possible  the  values 
from  a  steam  table  should  be  used  as  they  are  the  results  of  accu- 
rate measurements. 

87.  Latent  Heat. — After  water  is  raised  to  the  boiling-point, 
heat  must  be  added  to  change  it  into  steam.  This  heat,  called 
latent  heat,  varies  in  amount,  being  1091.7  B.t.u.  for  each  pound 
of  steam  formed  at  32°  F.  and  965.8  B.t.u.  for  each  pound 
formed  at  212°  F.  The  whole  amount  of  the  latent  heat  will  be 
absorbed  only  when  the  whole  pound  of  water  has  been  evapo- 
rated. If  the  water  is  being  evaporated  at  212°  F.  and  after 
reaching  the  evaporation  temperature  only  one-half  of  965.8  or 
482.9  B.t.u.  are  applied,  then  only  one-half  of  a  pound  of  water 
will  be  evaporated,  and  conversely,  if  we  extract  482.9  B.t.u. 
from  a  quantity  of  steam  at  212°  F.,  only  one-half  of  a  pound  will 
be  condensed. 

The  latent  heat  of  steam,  unlike  the  other  properties  so  far 
studied,  decreases  as  the  pressure  is  increased.  At  32°  F.  the 
latent  heat  is  1091.7  B.t.u.,  the  same  as  the  total  heat  at  this 
temperature,  since  there  would  be  no  heat  of  the  liquid  above 
32°  F.  if  the  water  boiled  at  32°  F.  It  seems  almost  incredible 
that  steam  can  be  formed  at  32°,  the  freezing  temperature  of 
water,  but  such  is  the  case.  It  can  be  done,  however,  only  in 
a  very  high  vacuum  (.089  Ib.  per  sq.  in.  absolute  pressure) 
wrhen  the  resistance  to  the  expansion  is  practically  all  removed. 
Under  such  conditions  it  is  possible  to  have  steam  rising  directly 
from  a  block  of  ice. 

The  decrease  of  the  latent  heat,  as  the  pressure  (and  con- 
sequently the  temperature)  increases,  amounts  to  .695  B.t.u. 
per  degree  and,  therefore,  the  latent  heat  per  pound  can  be 
expressed  by  the  formula: 

L  =  1091.7  -.695  0-32) 

where  t  is  the  temperature  of  the  steam,  and  L  is  the  corre- 
sponding latent  heat.  This  formula  gives  only  approximately 


PROPERTIES  OF  STEAM  107 

correct  results.  It  is  much  better  to  find  the  value  of  the  latent 
heat  in  a  steam  table  if  one  is  at  hand. 

It  must  be  firmly  impressed  on  the  mind  that  the  addition 
of  the  latent  heat  of  evaporation  and  the  consequent  trans- 
formation of  water  into  steam  has  no  effect  on  temperature 
and,  consequently,  the  steam  when  formed,  is  at  the  same  tem- 
perature as  the  boiling  water. 

88.  Total  Heat  of  Steam. — Steam,  as  we  know,  is  the  vapor 
formed  from  water  by  the  addition  of  heat.  The  water  must 
first  be  heated  to  a  certain  temperature,  depending  on  the  pressure 
which  is  exerted  on  it,  and,  after  reaching  this  point,  more  heat 
must  be  added  to  effect  the  change  of  state  from  water  into 
steam.  The  heat  required  for  the  generation  of  saturated  steam 
is  thus  divided  into  two  distinct  parts:  First,  the  Heat  of  the 
Liquid,  which  is  the  heat  that  the  water  must  have  above  a 
temperature  of  32°  F.  in  order  to  bring  it  to  the  boiling-point; 
and  second,  the  Latent  Heat,  which  is  the  heat  required  to  effect 
the  change  from  water  to  steam  without  change  of  temperature. 
The  sum  of  these  two  quantities  is  the  Total  Heat  of  1  Ib.  of  dry 
steam,  and  is  given  in  the  fourth  column  of  the  table. 

The  total  heat  of  steam  is  calculated  from  32°  as  a  basis,  and 
includes  all  of  the  heat  which  must  be  added  to  a  pound  of  water 
at  32°  in  order  to  bring  it  to  the  boiling  temperature  and  then 
evaporate  it  into  steam. 

A  study  of  the  steam  tables  will  reveal  the  fact  that  the  total 
heat  varies  but  little  for  even  a  large  variation  of  pressure.  There 
is  a  difference  of  only  44.6  B.t.u.  between  the  total  heat  of  steam 
at  atmospheric  pressure  and  at  a  pressure  of  150  Ib.  absolute. 

The  total  heat  can  be  expressed  in  terms  of  the  temperature  by 
a  very  simple  formula.  A  study  of  the  table  reveals  the  fact  that 
the  total  heat  increases  approximately  .305  B.t.u.  for  each  degree 
rise  in  the  temperature  of  evaporation.  At  32°  F.  the  total  heat 
is  1091.7  B.t.u.  The  total  heat  (H)  can,  therefore,  be  expressed 
by  the  formula: 

#  =  1091. 7  +  .305  0-32) 

where  t  is  any  temperature  of  evaporation  and  H  is  the  corre- 
sponding total  heat  of  steam.  The  term  (t  —32)  gives  the  tem- 
perature of  the  steam  above  32°  F.  The  total  heat  of  steam  is 
the  sum  of  the  two  items  heat  of  the  liquid  and  latent  heat,  and  as 
we  often  find  use  for  one  or  both  of  these  two  items  separately, 
columns  giving  each  of  them  are  found  in  the  tables. 


108  STEAM  BOILERS 

89.  Density  of  Steam. — There  are  two  remaining  columns  of 
the  tables.     The  information  contained  in  these  is  of  especial  use 
in  calculations  concerning  the  flow  of  steam  or  the  sizes  of  piping. 
The  density  of  steam  (or  its  weight  per  cubic  foot)  is,  of  course, 
directly  dependent  on  the  pressure  and  temperature  the  same 
as  any  other  gas.     An  approximate  formula  for  the  density  of 
steam  is: 

1.775  P 
T 

where  P  is  the  absolute  pressure 

T  is  the  absolute  temperature  (  =  t+460) 
and      D  is  the  corresponding  density  in  pounds  per  cubic  foot. 

90.  Specific  Volume. — The  specific  volume   is   the  space  in 
cubic  feet  occupied  by  1  Ib.  weight  of  steam.     This  is  the  recipro- 
cal of  the  density,  that  is,  it  is  1  divided  by  the  density.     Some 
steam  tables  do  not  give  both  the  density  and  specific  volume, 
since  they  are  so  closely  related.     If  the  specific  volume  of  steam 
at  atmospheric  pressure  is  26.39  cu.  ft.  per  pound,  the  density 
is  1  ^26. 39  =  .0379  Ib.  per  cubic  foot.     Likewise,  reversing  the 
same  example,  if  the  density  is  given  as  .0379,  the  specific  volume 
is  1  -f-. 0379  =  26.39  cu.  ft.  per  pound. 

91.  Expansion  of  Water  into  Steam. — Some  steam  tables  give 
a  column  showing  how  many  times  water  expands  in  changing 
into  steam.     This  is  not  of  much  practical  use,  and  if  wanted, 
can  be  easily  obtained  from  the  specific  volume  column.     One 

cubic  foot  of  water  weighs  62.4  Ib.,  or  1  Ib.  occupies  T^TI  cu.  ft. 

Then  the  specific  volume  of -steam  multiplied  by  62.4  will  give 
the  number  of  expansions  that  take  place  when  water  is  turned 
to  steam. 

Example :  How  many  cubic  feet  of  steam  at  atmospheric 
pressure  are  formed  from  a  cubic  foot  of  water? 

1  Ib.  of  steam  =26.39  cu.  ft.  (from  steam  table) 

1  cu.  ft.  of  water  =62.4  Ib. 

1  cu.  ft.  of  water  will  make  62.4  X26.39  =  1647  cu.  ft.  of  steam. 
Thus,  water  evaporated  under  atmospheric  pressure  expands 
1647  times  in  turning  into  steam.  The  greater  the  pressure  under 
which  the  steam  is  formed,  the  less  will  be  the  number  of  expan- 
sions which  it  undergoes. 

92.  Allowance  for  Feed  Water  Temperatures. — All  the  quan- 


PROPERTIES  OF  STEAM  109 

titles  of  heat  given  in  the  steam  table  are  calculated  from  water 
at  32°  F.  and  generally  it  is  necessary,  in  practical  problems,  to 
make  allowance  for  the  fact  that  the  feed  water  is  at  some  other 
temperature.  Thus,  if  we  wish  to  know  how  much  heat  must  be 
supplied  to  1  Ib.  of  feed  water  having  a  temperature  of  170°  in 
order  to  turn  it  into  steam  having  a  pressure  of  150  Ib.  absolute 
pressure,  we  must  remember  that  the  water  already  contains 

170-32  =  138   B.t.u. 

Now,  since  the  total  heat  of  steam  at  150  Ib.  pressure  absolute 
is  1191.2  B.t.u.  there  will  have  to  be  supplied  to  the  water  in  the 
boiler  only 

1191.2-138  =  1053.2  B.t.u. 

in  order  to  turn  it  into  steam.  Since  the  heat  of  the  liquid  at 
150  Ib.  pressure  is  329.6  B.t.u.,  only  329.6-138  =  191.6  B.t.u. 
need  be  supplied  to  the  water  to  bring  it  to  the  boiling  tempera- 
ture, but  the  entire  latent  heat,  861.6  B.t.u.,  has  to  be  supplied 
in  order  to  evaporate  it  into  steam. 

Some  people  obtain  the  part  of  the  heat  of  the  liquid  that 
must  be  supplied  in  the  boiler  by  subtracting  the  feed-water 
temperature  from  the  temperature  of  evaporation.  This  is  not 
as  accurate  as  the  method  just  outlined,  because  the  specific 
heat  of  water  is  not  as  near  1  at  high  temperatures  as  at  low 
temperatures. 

93.  Interpolation  from  Tables. — Interpolation  refers  to  the 
method  used  to  find  values  between  those  given  in  the  tables, 
as  for  example,  finding  the  latent  heat  at  44J  Ib.  absolute 
pressure.  The  table  gives  L  for  44  Ib.  and  for  45  Ib.  but  not 
for  44J  Ib.,  and  we  interpolate  to  get  the  value  for  44 J  Ib. 
which  would  be  halfway  between  922.8  and  921.8,  or  just  922.3. 
Suppose  we  wish  to  find  the  heat  of  the  liquid  at  120  Ib.  gage 
pressure.  The  table  gives  119.3  Ib.  and  120.3  Ib.,  the  corre- 
sponding values  of  h  being  320.5  and  321.1.  For  1  Ib.  change  in 
pressure,  h  changes  321.1 —320.5  =  .6.  Now  120  is  .7  Ib.  more 
than  119.3,  or  .3  Ib.  less  than  120.3.  We  can,  therefore,  add 
.7  of  .6  to  320.5,  or  subtract  .3  of  .6  from  321.1.  Either  way  we 
get  320.9  as  the  value  of  h  at  120  Ib.  gage  pressure. 

In  interpolating,  remember  that  L  and  v  decrease  as  the  pres- 
sure increases  and  that  all  other  items  in  the  table  increase. 
For  most  calculations  it  is  sufficiently  accurate  to  take  the  near- 
est value  given  in  the  table  without  bothering  to  interpolate. 


110 


STEAM  BOILERS 


PROPERTIES  OF  SATURATED  STEAM 


Absolute 
pressure 

Gage 
pressure 

Tempera- 

Total  heat  above 
32° 

Latent 

Weight 
of  1  cu. 

Volume  of 
1  Ib.  of 

inlb. 
per 

inlb. 
per 

Fahren- 
heit 

In  the 

In  the 

heat, 
H-h. 

ft.  of 
steam  in 

steam    in 
cu   ft  =  -- 

sq.  in. 

sq.  in. 

steam 

water 

Ib. 

w 

P 

t 

H 

h 

L 

w 

v 

0.089 

-14.611 

32.0 

1091.7 

0.0 

1091.7 

.00030 

3333.3 

0.5 

-14.2 

79.9 

1106.3 

47.9 

1058.4 

.00157 

636.9 

1 

-13.7 

102.0 

1113.1 

70.0 

1043  .  1 

.0030 

333.3 

1.5 

-13.2 

115.9 

1117.3 

84.0 

1033.3 

.0044 

227.3 

2 

-12.7 

126.3 

1120.5 

94.4 

1026  .  1 

.0058 

172.4 

2.5 

-12.2 

134.6 

1123.0 

102.8 

1020.2 

.0071 

140.8 

3 

-11.7 

141.6 

1125.1 

109.8 

1015.3 

.0085 

117.6 

3.5 

-11.2 

147.7 

1127.0 

116.0 

1011.0 

.0098 

102.0 

4 

-10.7 

153.1 

1128.6 

121.5 

1007.1 

.0111 

90.09 

4.5 

-10.2 

157.9 

1130.1 

126.3 

1003  .  8 

.0124 

80.65 

5 

-   9.7 

162.3 

1131.4 

130.7 

1000.7 

.0137 

72.99 

5.5 

-    9.2 

166.4 

1132.7 

134.8 

997.9 

.0150 

66.67 

6 

-   8.7 

170.1 

1133.8 

138.6 

995.2 

.0163 

61.35 

6.5 

-   8.2 

173.6 

1134.9 

142.1 

992.8 

.0176 

56.82 

7 

-   7.7 

176.9 

1135.9 

145.4 

990.5 

.0189 

52.91 

7.5 

-   7.2 

180.0 

1136.8 

148.5 

988.3 

.0202 

49.50 

8 

-   6.7 

182.9 

1137.7 

151.5 

986.2 

.0214 

46.73 

8.5 

-   6.2 

185.7 

1138.6 

154.3 

984.3 

.0227 

44.05 

9 

-   5.7 

188.3 

1139.4 

156.9 

982.5 

.0239 

41.84 

9.5 

-   5.2 

190.8 

1140.1 

159.4 

980.7 

.0252 

39.68 

10 

-   4.7 

193.2 

1140.9 

161.8 

979.1 

.0264 

37.88 

10.5 

-   4.2 

195.6 

1141.6 

164.2 

977.4 

.0276 

36.23 

11 

-   3.7 

197.8 

1142.3 

166.5 

975.8 

.0288 

34.72 

11.5 

-   3.2 

199.9 

1142.9 

168.6 

974.3 

.0301 

33.22 

12 

-    2.7 

202.0 

1143.6 

170.7 

972.9 

.0313 

31.95 

12.5 

-   2.2 

204.0 

1144.2 

172.7 

971.5 

.0326 

30.67 

13 

-    1.7 

205.9 

1144.7 

174.7 

970.0 

.0338 

20.59 

13.5 

-    1.2 

207.8 

1145.3 

176.6 

968.7 

.0350 

28.57 

14 

-   0.7 

209.6 

1145.9 

178.4 

967.5 

.0362 

27.62 

14.7 

0.0 

212.0 

1146.6 

180.8 

965.8 

.0379 

26.39 

15 

+   0.3 

213.0 

1146.9 

181.8 

965.1 

.0386 

25.91 

16 

1.3 

216.3 

1147.9 

185.2 

962.7 

.0410 

24.39 

17 

2.3 

219.4 

1148.9 

188.3 

960.6 

.0434 

23.04 

18 

3.3 

222.4 

1149.8 

191.3 

958.5 

.0458 

21.83 

19 

4.3 

225.2 

1150.6 

194.1 

956.5 

.0482 

20.75 

20 

5.3 

227.9 

1151.4 

196.8 

954.6 

.0506 

19.76 

21 

6.3 

230.5 

1152.2 

199.5 

952.7 

.0530               18.87 

22 

7.3 

233.1 

1153.0 

202.1 

950.9 

.0553 

18.08 

23 

8.3 

235.5 

1153.8 

204.5 

949.3 

.0577 

17.33 

24 

9.3 

237.8 

1154.5 

206.8 

947.7 

.0601 

16.64 

25 

10.3 

240.0 

1155.1 

209.1 

946.0 

.0624 

16.03 

26 

11.3 

242.2 

1155.8 

211.3 

944  .  5 

.0648 

15.43 

27 

12.3 

244.3 

1156.5 

213.4 

943.1 

.0671 

14.90 

28 

13.3 

246.3 

1157.1 

215.5 

941.6 

.0695 

14.39 

29 

14.3 

248.3 

1157.7 

217.5 

940.2 

.0718 

13.93 

PROPERTIES  OF  STEAM 


111 


PROPERTIES  OF  SATURATED  STEAM— Continued 


Absolute 
pressure 
inlb. 
per 

Gage 
pressure 
in  Ib. 
per 

Tempera- 
ture, 
Fahren- 
heit 

Total  heat  above 
32°  F. 

Latent 
Heat 
H-h. 

Weight 
of  1  cu. 
ft.  of 
steam 

in   Ih 

Volume  of 
1    Ib.    of 
steam   in 

cu.    ft.  =  - 

In  the 

In  the 

sq.  in. 

sq.  in. 

steam 

water 

in  ID. 

w 

P 

t 

H 

h 

L 

w 

v 

30 

15.3 

250.3 

1158.3 

219.5 

938.8 

.0741 

13.50 

31 

16.3 

252.2 

'1158.9 

221.4 

937.5 

.0764 

13.09 

32 

17.3 

254.0 

1159.4 

223.2 

936.2 

.0787 

12.71 

33 

18.3 

255.8 

1160.0 

225.0 

935.0 

.0810 

12.35 

34 

19.3 

257.5 

1160.5 

226.8 

933.7 

.0833 

12.00 

35 

20.3 

259.2 

1161.0 

228.5 

932.5 

.0856 

11.68 

36 

21.3 

260.9 

1161.5 

230.2 

931.3 

.0879 

11.38 

37 

22.3 

262.5 

1162.0 

231.9 

930.1 

.0902 

11.09 

38 

23.3 

264.1 

1162.5 

233.5 

929.0 

.0925 

10.81 

39 

24.3 

265.6 

1162.9 

235.0 

927.9 

.0948 

10.55 

40 

25.3 

267.1 

1163.4 

236.5 

926.9 

.0971 

10.30 

41 

26.3 

268.6 

1163.9 

238.0 

925.9 

.0993 

10.07 

42 

27.3 

270.1 

1164.3 

239.5 

924.8 

.1016 

9.843 

43 

28.3 

271.5 

1164.7 

241.0 

923.7 

.1039 

9.625 

44 

29.3 

272.9 

1165.2 

242.4 

922.8 

.1062 

9.416 

45 

30.3 

274.3 

1165.6 

243.8 

921.8 

.1085 

9.217 

46 

31.3 

275.7 

1166.0 

245.2 

920.8 

.1108 

9.025 

47 

32.3 

277.0 

1166.4 

246.6 

919.8 

.1130 

8.850 

48 

33.3 

278.3 

1166.8 

247.9 

918.9 

.1152 

8.681 

49 

34.3 

279.6 

1167.2 

249.2 

918.0 

.1175 

8.511 

50 

35.3 

280.9 

1167.6 

250.5 

917.1 

.1197 

8.354 

51 

36.3 

282.1 

1168.0 

251.8 

916.2 

.1220 

8.197 

52 

37.3 

283.3 

1168.3 

253.0 

915.3 

.1242 

8.052 

53 

38.3 

284.5 

1168.7 

254.2 

914.5 

.1264 

7.911 

54 

39.3 

285.7 

1169.1 

255.4 

913.7 

.1287 

7.770 

55 

40.3 

286.9 

1169.4 

256.6 

912.8 

.1309 

7.639 

56 

41.3 

288.1 

1169.8 

257.8 

912.0 

.1332 

7.508 

57 

42.3 

289.2 

1170.1 

259.0 

911.1 

.1354 

7.386 

58 

43.3 

290.3 

1170.5 

260.1 

910.4 

.1376 

7.267 

59 

44.3 

291.4 

1170.8 

261.2 

909.6 

.1398 

7.153 

60 

45.3 

292.5 

1171.2 

262.3 

908.9 

.1420 

7.042 

61 

46.3 

293.6 

1171.5 

263.4 

908.1 

.1443 

6.930 

62 

47.3 

294.7 

1171.8 

264.5 

907.3 

.1465 

6.826 

63 

48,3 

295.7 

1172.1 

265.6 

906.5 

.1487 

6.725 

64 

49.3 

296.8 

1172.5 

266.7 

905.8 

.1509 

6.627 

65 

50.3 

297.8 

1172.8 

267.7 

905.1 

.1531 

6.532 

66 

51.3 

298.8 

1173.1 

268.7 

904.4 

.1553 

6.439 

67 

52.3 

299.8 

1173.4 

269.7 

903.7 

.1575 

6.349 

68 

53.3 

300.8 

1173.7 

270.7 

903.0 

.1597 

6.262 

69 

54.3 

301.8 

1174.0 

271.7 

902.3 

.1619 

6.177 

70 

55.3 

302.7 

1174.3 

272.7 

901.6 

.1641 

6.094 

71 

56.3 

303.7 

1174.6 

273.7 

900.9 

.1663 

6.013 

72 

57.3 

304.6 

1174.8 

274.7 

900.1 

.1685 

5.935 

73 

58.3 

305.6 

1175.1 

275.7 

899.4 

.1707 

5.858 

74 

59.3 

306.5 

1175.4 

276.6 

898.8 

.1729 

5.784 

112 


STEAM  BOILERS 


PROPERTIES  OF  SATURATED  STEAM— Continued 


Absolute 
pressure 
inlb. 
per 

Gage 
pressure 
inlb. 
per 

Tempera- 
ture, 
Fahren- 
heit. 

Total  heat  above 
32°  F. 

Latent 
heat, 
H-h. 

Weight  of 
1  cu.  ft. 
of  steam 
inlb. 

Volume 
of  1  Ib.  of 
steam  in 

cu.  ft.  =- 

In  the 

In  the 

sq.  in. 

sq.  in. 

steam 

water 

w 

P 

t 

H 

h 

L 

w 

V 

75 

60.3 

307.4 

1175.7 

277.5 

898.2 

.1751 

5.711 

76                  61.3 

308.3 

1176.0 

278.4- 

897.6 

.1773 

5.640 

77                  62.3 

309.2 

1176.2 

279.3 

896.9 

.1795 

5.571 

78                  63.3 

310.1 

1176.5 

280.2 

896.3 

.1817 

5.504 

79                  64.3 

311.0 

1176.8 

281.1 

895.7 

.1839 

5.438 

80                  65.3 

311.8 

1177.0 

282.0 

895.0 

.1860 

5.376 

81                  66.3 

312.7 

1177.3 

282.9 

894.4 

.1882 

5.313 

82                  67.3 

313.5 

1177.6 

283.7 

893.9 

.1904 

5.252 

83                  68.3 

314.4 

1177.8 

284.6 

893.2 

.1926 

5.192 

84                  69.3 

315.2 

1178.1 

285.5 

892.6 

.1948 

5.133 

85                  70.3 

316.0 

1178.3 

286.3 

892.0 

.1970 

5.076 

86                  71.3 

316.8 

1178.6 

287.1 

891.5 

.1991 

5.023 

87                  72.3 

317.7 

1178.8 

288.0 

890.8 

.2013 

4.968 

88                  73.3 

318.5 

1179.1 

288.8 

890.3 

.2035 

4.914 

89                  74.3 

319.3 

1179.3 

289.6 

889.7 

.2056 

4.864 

90                  75.3 

320.1 

1179.6 

290.4 

889.2 

.2078 

4.812 

91                  76.3 

320.8 

1179.8 

291.2 

888.6 

.2100 

4.762 

92                  77.3 

321.6 

1180.0 

292.0 

888.0 

.2122 

4.713 

93                   78.3     |       322.4 

1180.3 

292.8 

887.5 

.2143 

4.666 

94 

79.3            323.1 

1180.5 

293.6 

886.9 

.2165 

4.619 

95 

80.3 

323.9 

1180,7 

294.4 

886.3 

.2186 

4.575 

96                  81.3 

324.6 

1180.9 

295.1 

885.8 

.2208 

4.529 

97                   82.3            325.4 

1181.2 

295.9 

885.3 

.2229 

4.486 

98 

83.3 

326.1 

1181.4 

296.6 

884.8 

.2251 

4.442 

99 

84.3 

326.9 

1181.6 

297.4 

884.2 

.2273 

4.399 

100                  85.3 

327.6 

1181.9 

298.1 

883.8 

.2294 

4.359 

101                  86.3 

328.3 

1182.1 

298.8 

883.3 

.2316 

4.318 

102                  87.3 

329.0 

1182.3 

299.6 

882.7 

.2337 

4.279 

103                   88.3 

329.7 

1182.5 

300.3 

882.2 

.2359 

4.239 

104                  89.3 

330.4 

1182.7 

301.0 

881.7 

.2380                 4.202 

105                  90.3 

331.1 

1182.9 

301.7 

881.2 

.2402                 4.163 

106 

91.3 

331.8 

1183.1 

302.4 

880.7 

.2423                 4.127 

107 

92.3 

332.5 

1183.4 

303.1 

880.3 

.  2445                 4  .  909 

108 

93.3 

333.2 

1183.6 

303.8 

879.8 

.2466                 4.055 

109 

94.3            333.9 

1183.8 

304.5 

879.3 

.2488                 4.019 

110 

95.3            334.5 

1184.0 

305.2 

878.8 

.2509                 3.986 

111 

96.3            335.2 

1184.2 

305.9 

878.3 

.2530                 3.933 

112 

97.3 

335.9 

1184.4 

306.6 

877.8 

.2552                 3.918 

113 

98.3 

336.5 

1184.6 

307.3 

877.3 

.2573 

3.887 

114 

99.3 

337  .  2 

1184.8 

308.0 

876.8 

.  2595 

3.854 

115 

100.3 

337.8 

1185.0 

308.6 

876.4 

.2616 

3.823 

116 

101.3 

338.5 

1185.2 

309.3 

875.9 

.2637 

3.792 

117 

102.3 

339.1 

1185.4 

309.9 

875.5 

.2659 

3.761 

118 

103.3 

339.8 

1185.6 

310.6 

875.0 

.2680 

3.731 

119 

104.3 

340.4 

1185.8 

311.2 

874.6 

.2702 

3.701 

PROPERTIES  OF  STEAM 


113 


PROPERTIES  OF  SATURATED  STEAM— Continued 


Total  heat  above 

Absolute 
pressure 
inlb. 
per 

Gage 
pressure 
in  Ib. 
per 

Tempera- 
ture, 
Fahren- 
heit 

32°  F. 

Latent 
heat, 
H-h. 

Weight  of 
1  cu.  ft. 
of  steam 
inlb. 

Volume 
of    1  Ib. 
steam  in 

cu.  ft.  •=•- 

In  the 

In  the 

sq.  in. 

sq.  in. 

steam 

water 

w 

P 

t 

H 

h 

L 

w 

V 

120 

105.3 

341.0 

1185.9 

311.9 

874.0 

.2723 

3.672 

121 

106.3 

341.7 

1186.2 

312.6 

873.6 

.2744 

3.644 

122 

107.3 

342.3 

1186.3 

313.2 

873.1 

.2765 

3.617 

123 

108.3 

342.9 

1186.5 

313.8 

872.7 

.2787 

3.588 

124 

109.3 

343.5 

1186.7 

314.4 

872.3 

.2808 

3.561 

125 

110.3 

344.1 

1186.9 

315.0          871.9 

.2829 

3.535 

126 

111.3 

344.7 

1187.1 

315.6          871.5         .2850       |          3.509 

127 

112.3 

345.3 

1187.3 

316.3          871.0 

.2872                 3.482 

128 

113.3 

345.9 

1187.4 

316.9          870.5 

.2893 

3.457 

129 

114.3 

346.5 

1187.6 

317.5 

870.1 

.2914 

3.432 

130 

115.3 

347.1 

1187.8 

318.1 

869.7 

.2935                3.407 

131 

116.3 

347.7 

1188.0 

318.7 

869.3 

.2957 

3.382 

132 

117.3 

348.3 

1188.2 

319.3 

868.9 

.2978 

3.358 

133 

118.3 

348.8 

1188.3 

319.9 

868.4 

.2999 

3.334 

134 

119.3 

349.4 

1188.5 

320.5 

868.0 

.3020 

3.311 

135 

120.3 

350.0 

1188.7 

321.1 

867.6 

.3042 

3.287 

136 

121.3 

350.6 

1188.9 

321.7 

867.2 

.3063 

3.265 

137 

122.3 

351.1 

1189.0 

322.3 

866.7 

.3084 

3.243 

138 

123.3 

351.7 

1189.2 

322.9 

866.3 

.3105 

3.221 

139 

124.3 

352.3 

1189.4 

323.5 

865.9 

.3126 

3.199 

140 

125.3 

352.8 

1189.5 

324.0 

865.5 

.3147 

3.178 

141 

126.3 

353.4 

1189.7 

324.6 

865.1 

.3169 

3.156 

142 

127.3 

353.9 

1189.9 

325.1 

864.8 

.3190 

3.135 

143 

128.3 

354.5 

1190.1 

325.7 

864.4 

.3211 

3.114 

144 

129.3 

355.0 

1190.2 

326.3 

863.9 

.3232 

3.094 

145 

130.3 

355.6 

1190.4 

326.9 

863.5 

.3253 

3.074 

146 

131.3 

356.1 

1190.6 

327.4 

863.2 

.3274 

3.054 

147 

132.3 

356.7 

1190.7 

328.0 

862.7 

.3295 

3.035 

148 

133.3 

357.2 

1190.9 

328.5 

862.4 

.3316 

3.016 

149 

134.3 

357.7 

1191.0 

329.0 

862.0 

.3337 

2.997 

150 

135.3 

358.2 

1191.2 

329.6 

861.6 

.3358 

2.978 

151 

136.3 

358.8 

1191.4 

330.2 

861.2 

.3379 

2.959 

152 

137.3 

359.3 

1191.5 

330.7 

860.8 

.3400 

2.941 

153 

138.3 

359.8 

1191.7 

331.2 

860.5 

.3421 

2.923 

154 

139.3 

360.3 

1191.8 

331.7 

860.1 

.3442 

2.905 

155 

140.3 

360.8 

1192.0 

332.2 

859  .  8 

.3463 

2.888 

156 

141.3 

361.4 

1192.2 

332.8 

859.4 

.3484 

2.870 

157 

142.3 

361.9 

1192.3 

333.3 

859.0 

.3504 

2.854 

158 

143.3 

362.4 

1192.5 

333.9 

858.6 

.3525 

2.837 

159 

144.3 

362.9 

1192.6 

334.4 

858.2 

.3546 

2.820 

160 

145.3 

363.4 

1192.8 

334.9 

857.9 

.3567 

2.803 

161 

146.3 

363.9 

1192.9 

335.4 

857.5 

.3588 

2.787 

162 

147.3 

364.4 

1193.1 

335.9 

857.2 

.3609 

2.771 

163 

148.3 

364.9 

1193.2 

336.4 

856.8 

.3630 

2.755 

164 

149.3 

365.4 

1193.4 

336.9 

856.5 

.3651 

2.739 

165 

150.3 

365.9 

1193.5 

337.4 

856.1 

•    .3672 

2.723 

166 

151.3 

366.3 

1193.7 

337.9 

855.8 

.3693 

2.708 

167 

.     152.3 

366.8 

1193.8 

338.4 

855.4 

.3714                 2.693 

11 


114 


STEAM  BOILERS 


PROPERTIES  OF  SATURATED  STEAM— Continued 


Total  heat  above 

Absolute 
pressure 
inlb. 
per 

Gage 
pressure 
inlb. 
per 

Temperar 
ture, 
Fahren- 
heit 

32°  F. 

Latent 
heat 
H-h. 

Weight  of 
1  cu.  ft. 
of  steam 
inlb. 

Volume 
of  1  Ib. 
steam  in 

cu.  ft.   =- 

In  the 

In  the 

sq.  in. 

sq.  in. 

steam 

water 

w 

P 

t 

H 

h 

L 

w 

V 

168 

153.3 

367.3 

1194.0 

338.9 

855.1 

.3734 

2.678 

169 

154.3            367.8 

1194.1 

339.4 

854.7         .3755                 2.663 

170 

155.3            368.3 

1194.3 

339.9 

854.4        .3776                2.648 

171 

156.3            368.7 

1194.4 

340.4 

-854.0 

.3797                 2.634 

172 

157.3     !       369.2 

1194.5 

340.9 

853.6         .3818                 2.619 

173 

158.3            369.7 

1194.7 

341.4 

853.3         .3839                 2.605 

174 

159.3            370.1 

1194.8        341.8 

853.0         .3860                 2.591 

175 

160.3            370.6 

1195.0        342.3 

852.7         .3880 

2.577 

176 

161.3     i       371.1 

1195.1 

342.8 

852.3         .3901 

2.563 

177 

162.3            371.5 

1195.2        343.3 

851.9 

.3922 

2.550 

178 

163.3            372.0 

1195.4        343.8 

851.6         .3943 

2.536 

179 

164.3            372.5 

1195.6 

344.3 

851.3 

.3963 

2.523 

180 

165.3     1       372.9 

1195.7 

344.7 

851.0 

.3984 

2.510 

181 

166.3     !       373.4 

1195.8 

345.2 

850.6 

.4005 

2.497 

182 

167.3 

373.8 

1195.9 

345.7 

850.2 

.4026 

2.484 

183 

168.3 

374.3 

1196.1 

346.2 

849.9 

.4047 

2.471 

184 

169.3 

374.7 

1196.2 

346.6 

849.6 

.4067 

2.459 

185 

170.3 

375.2 

1196.4 

347.1 

849.3 

.4088 

2.446 

186 

171.3 

375.6 

1196.5 

347.5 

849.0 

.4109 

2.434 

187 

172.3 

376.0 

1196.6 

348.0 

848.6 

.4130 

2.421 

188 

173.3 

376.5 

1196.8 

348.5 

848.3 

.4151 

2.409 

189 

174.3 

376.9 

1196.9 

348.9 

848.0 

.4171 

2.398 

190 

175.3 

377.4 

1197.0 

349.4 

847.6 

.4192 

2.385 

191 

176.3 

377.8 

1197.2 

349.8 

847.4 

.4213 

2.374 

192 

177.3 

378.3 

1197.3 

350.3 

847.0 

.4234 

2.362 

193 

178.3 

378.7 

1197.4 

350.7 

846.7 

.4254 

2.351 

194 

*179.3 

379.1 

1197.6 

351.2 

846.4 

.4275 

2.339 

195 

180.3 

379.6 

1197.7 

351.7 

846.0 

.4296 

2.328 

196 

181.3 

380.0 

1197.8 

352.1 

845.7 

.4317 

2.316 

197 

182.3            380.4 

1198.0 

352.5 

845.5 

.4338 

2.305 

198 

183.3            380.8 

1198.1 

352.9 

845.2 

.4359 

2.294 

199 

184.3            381.3 

1198.2 

353.4 

844.8 

.4380 

2.283 

200 

185.3            381.7 

1198.4 

353.8 

844.6 

.4400 

2.273 

205 

190.3            383.8 

1199.0 

356.0 

843.0 

.4504 

2.220 

210 

195.3            385.8 

1199.6 

358.1 

841.5 

.4608 

2.170 

215 

200.3            387.8 

1200.2        360.2 

840.0 

.4712 

2.122 

220 

205.3            389.8 

1200.8 

362.2 

838.6 

.4816                 2.076 

225 

210.3            391.7 

1201.4 

364.2 

837.2 

.4920                 2.033 

230 

215.3            393.6 

1202.0 

366.2 

835.8 

.5024                 1.990 

240 

225.3            397.3 

1203.1 

370.1 

833.0 

.5231                 1.912 

250 

235.3 

400.9 

1204.2 

373.8 

830.4 

.5439 

1.839 

260 

245.3 

404.4 

1205.3 

377.5 

827.8 

.  5646 

1.771 

270 

255.3            407.8 

1206.3 

381.0 

825.3 

.5854 

1.708 

280 

265.3            411.1 

1207.3 

384.4 

822.9 

.6061 

1.650 

290 

275.3 

414.3 

1208.3 

387.8 

820.5 

.  6268                 1  .  595 

300 

285.3            417.4 

1209.2        391.0 

818.2 

.6475                 1.544 

325 

310.3            424.8 

1211.5        398.7 

812.8 

.6990                 1.431 

350 

•335.3            431.8 

1213.6        406.0 

807.6 

.7505                 1.332 

I 

CHAPTER  VIII 
ACTUAL  AND  EQUIVALENT  EVAPORATION 

94.  Wet  Steam. — When  heat  is  applied  to  a  boiler  slowly  the 
temperature  of  the  water  contained  in  it  is  raised  gradually 
until  it  reaches  the  boiling-point.  If  the  application  of  heat  is 
continued  the  water  begins  to  boil  slowly.  Under  these  condi- 
tions the  bubbles  of  steam  formed  next  to  the  heating  surface 
are  small  and,  as  they  become  detached  from  the  heating  surface, 
rise  slowly  to  the  surface  of  the  water.  Upon  reaching  the 
surface,  the  bubbles  burst  and  empty  their  steam  into  the  space 
above  the  surface  of  the  water.  Steam  formed  in  this  manner 
will  be  dry  saturated  steam. 

If,  on  the  other  hand,  heat  is  supplied  to  the  water  so  rapidly 
as  to  cause  it  to  boil  violently,  the  steam  bubbles  formed  on  the 
heating  surface  will  be  large  and,  when  they  become  detached, 
will  rise  to  the  surface  more  rapidly.  As  the  steam  bubbles 
reach  the  surface  they  burst  violently  and  the  water  which  forms 
the  film  around  them  is  thrown  into  the  steam  space  in  the  form 
of  very  small  particles  of  water.  These  particles  of  water  are  so 
small  and  light  that  they  remain  suspended  in  the  mass  of  steam 
and  cause  it  to  be  wet.  Thus  a  boiler  may  form  either  dry  or 
wet  steam  depending  upon  the  rate  at  which  the  steam  is  formed. 

The  importance  of  a  large  disengagement  surface  may  now  be 
understood.  If  the  disengagement  surface  is  small  in  proportion 
to  the  amount  of  steam  formed,  a  great  many  steam  bubbles 
will  burst  in  a  small  area,  keeping  the  surface  of  the  water  in 
violent  commotion  and  causing  more  of  it  to  be  thrown  into  the 
steam.  But  if  the  disengagement  area  is  large,  a  smaller  number 
of  steam  bubbles  will  burst  in  a  given  area  and  the  surface  of  the 
water  will  not  be  disturbed  very  much. 

If  the  water  is  boiling  so  violently  as  to  throw  large  quantities 
of  water  into  the  steam  space,  or  if  the  water  foams,  the  boiler  is 
said  to  "  prime."  Foaming  is  usually  caused  by  the  presence  of 
some  impurity  in  the  water  which  causes  a  scum  to  form  over  its 
surface.  The  presence  of  a  scum  over  the  surface  prevents  the 
steam  from  being  discharged  readily  into  the  steam  space,  hence 

115 


116  STEAM  BOILERS 

it  collects  under  the  layer  of  scum  until  enough  is  present  to 
raise  large  portions  of  it  into  the  steam  space,  where  the  rapidly 
moving  current  of  steam  carries  it  into  the  steam  pipes  leading 
from  the  boiler. 

The  moisture  which  is  suspended  in  wet  steam  is  not  in  the 
form  of  vapor  since  it  has  not  been  evaporated,  but  it  still  exists 
in  the  form  of  water  which  is  at  the  temperature  of  the  steam. 
Wet  steam  is  thus  composed  of  two  parts,  one  of  saturated  steam 
and  the  other  of  water. 

That  part  of  wet  steam  which  is  in  the  form  of  water  has 
received  only  enough  heat  to  raise  its  temperature  to  the  boiling- 
point.  If  its  temperature  was  originally  32°  it  has,  therefore, 
received  the  "heat  of  the  liquid."  That  part  of  the  wet  steam 
which  is  in  the  form  of  saturated  vapor  or  steam  has  received 
enough  heat  to  not  only  raise  its  temperature  to  the  boiling- 
point,  but  also  enough  to  evaporate  it.  If  the  water  from  which 
it  was  formed  was  originally  at  32°  it  contains  the  "total  heat" 
as  given  in  the  steam  table. 

To  illustrate  the  way  in  which  the  heat  contained  in  wet  steam 
is  divided  between  the  moisture  and  the  steam,  consider  1  Ib. 
of  wet  steam  formed  under  a  pressure  of  120  Ib.  per  sq.  in. 
absolute,  and  suppose  the  pound  of  wet  steam  to  consist  of  1/5 
or  0.2  of  a  pound  of  moisture  and  4/5  or  0.8  of  a  pound  of  satu- 
rated steam.  The  0.2  of  a  pound  of  moisture  has  received 
enough  heat  to  raise  its  temperature  to  the  boiling-point.  If  its 
original  temperature  was  32°,  each  pound  will  receive  311.9 
B.t.u.  which  is  the  heat  of  the  liquid  corresponding  to  a  pres- 
sure of  120  Ib.  per  sq.  in.  absolute.  The  0.2  of  a  pound  of 
moisture  will,  therefore,  contain  0.2X311.9  =  62.38  B.t.u.  The 
0.8  of  a  pound  of  saturated  steam  has  received  not  only  enough 
heat  to  bring  it  to  the  boiling-point  but  also  enough  to  evaporate 
it.  The  amount  of  heat  required  to  bring  it  to  the  boiling-point 
is  0.8x311.9  =  249.52  B.t.u.  and  the  amount  required  to  evapo- 
rate it  will  be  0.8  of  the  latent  heat  of  1  Ib.  or  0.8x874  =  699.2 
B.t.u.  Therefore,  the  1  Ib.  of  wet  steam  contains  62.38  +249.52 
+  699.2  =  1011.1  B.t.u. 

Since  the  whole  pound  of  water  must  be  heated  to  the  boiling 
point  while  only  a  fraction  of  the  pound  has  to  receive  the  latent 
heat  of  evaporation,  the  above  calculation  may  be  combined 
into  the  following  formula 

Hw=h+qL 


ACTUAL  AND  EQUIVALENT  EVAPORATION    117 
in  which  Hw  is  the  number  of  B.t.u.  in  a  pound  of  wet  steam, 

h  is  the  heat  of  the  liquid, 
L  is  the  latent  heat  of  evaporation, 
q  is  the  fraction  of  the  whole  pound  which  is  dry 
saturated  steam. 

Applying  this  formula  to  the  above  problem 


tf*  =311.9  +.8X874 

=  311.9  +  699.2  =  1011.1  B.t.u. 

which  is  the  same  result  as  obtained  before. 

Comparing  the  amount  of  heat  contained  in  a  pound  of  the 
wet  steam  specified  above  with  that  contained  in  a  pound  of  dry 
steam  we  see  that  the  wet  steam  contains  only  1011.1  B.t.u. 
while,  if  it  had  been  dry,  it  would  contain  1185.9  B.t.u.  In  other 
words,  the  wet  steam  contains  174.8  less  heat  units  than  the 
dry  steam,  and  the  more  moisture  there  is  suspended  in  steam 
the  fewer  heat  units  each  pound  of  it  will  contain. 

Since  a  pound  of  wet  steam  contains  less  heat  than  a  pound  of 
dry  steam  there  is  a  disadvantage  in  operating  a  boiler  in  such 
a  manner  as  to  produce  wet  steam,  because  a  greater  weight  of 
steam  must  be  handled  in  order  to  transfer  a  certain  number  of 
heat  units  from  the  boiler  to  the  engines.  This  involves  larger 
apparatus  and  the  handling  of  more  feed  water.  If  the  amount 
of  moisture  in  the  steam  becomes  excessive,  that  is,  if  the  boiler 
primes,  there  is  danger  of  flooding  the  engine  cylinder  and  of 
damaging  the  piping  by  water-hammer. 

95.  Quality  of  Steam.  —  The  factor  q  in  the  above  formula  for 
finding  the  heat  contained  in  wet  steam  is  called  the  quality 
factor.  The  quality  of  steam  (sometimes  called  the  dryness  of 
the  steam)  is  the  portion  of  the  total  weight  of  steam  which  is 
in  the  form  of  steam  or  vapor,  as  distinguished  from  that  portion 
which  is  in  the  form  of  moisture.  The  quality  is  expressed  as  a 
per  cent  of  the  total  weight.  Thus  in  the  example  given  above 
the  quality  .or  dryness,  g,  is  .80  or  80  per  cent.  If  one-half  of  the 
pound  of  steam  had  been  water,  the  other  half  being  in  the  form 
of  steam,  the  quality  would  have  been  .50  or  50  per  cent,  and 
if  the  steam  had  contained  1/4  water  and  3/4  steam  its  quality 
would  have  been  .75  or  75  per  cent.  If  the  steam  had  been 
perfectly  dry,  all  of  it  would  have  been  in  the  form  of  vapor  or 


118  STEAM  BOILERS 

steam  and  its  quality  would,  therefore,  be  1.00  or  100  per  cent. 
The  wetness  of  steam  is  100  per  cent  minus  the  per  cent  of  dry- 
ness  or  (100 -g). 

In  applying  the  quality  factor  to  the  heat  contained  in  steam  it 
should  be  remembered  that  the  quality  does  not  apply  to  the  total 
heat  as  given  in  the  steam  table  but  only  to  the  latent  heat.  The  heat 
of  the  liquid  is  the  same  whether  the  steam  is  wet  or  dry  but  the 
latent  heat  of  a  pound  of  steam  will  be  ^ss  if  the  steam  is  wet 
than  if  it  is  dry.  For  this  reason  the  formula  for  the  heat  in  a 
pound  of  wet  steam  must  take  the  form 

Hw  =  (h+qL) 

Under  ordinary  operating  conditions,  power  boilers  will 
generate  steam  having  a  quality  from  97  to  100  per  cent.  If 
forced  above  their  rated  loads  the  quality  may  fall  considerably 
below  this,  depending  upon  how  hard  the  boilers  are  forced. 
Steam  which  has  a  quality  of  not  less  than  98  per  cent  is  called 
" commercially  dry"  steam. 

96.  Steam  Calorimeters. — The  quality  of  steam  may  be  meas- 
ured by  means  of  an  instrument  called   a  steam   calorimeter. 
There  are  two  forms  of  steam  calorimeters  called  respectively 
the  Separating  Calorimeter  and  the  Throttling  Calorimeter. 

97.  Separating  Calorimeter. — The  separating  calorimeter  shown 
in  cross-section  in  Fig.  68  separates  the  water  from  the  steam 
mechanically,  collecting  the  water  at  one  place  and  allowing 
the  steam,  now  free  of  moisture,  to  pass  off  at  another.     Since 
water  is  heavier  than  an  equal  volume  of  steam,  if  the  direction 
in  which  a  mixture  of  steam  and  water  is  flowing  is  suddenly 
changed,  the  particles  of  water  will  be  thrown  out  of  the  steam. 
The  water  being  heavy,  tends  to  continue  in  a  straight  line,  while 
the  steam  being  lighter,  can  have  its  directions  of  flow  changed 
more  readily.     This  principle  is  made  use  of  in  the  separating 
calorimeter. 

The  body  of  the  separating  calorimeter  consists  of  a  double 
walled  hollow  chamber  with  a  steam  pipe  connection  leading 
through  the  top  into  the  inner  chamber.  A  metal  basket  with 
perforated  sides  is  suspended  in  the  upper  part  of  the  inner  cham- 
ber with  its  bottom  a  short  distance  below  the  end  of  the  steam 
connection.  The  inner  chamber  is  connected  to  the  outer  one 
through  an  opening  located  at  the  top  of  the  perforated  metal 
basket.  The  outer  chamber,  located  between  the  two  walls  of 


ACTUAL  AND  EQUIVALENT  EVAPORATION    119 

the  body  of  the  calorimeter,  has  an  outlet  to  the  atmosphere 
through  a  small  hole  in  the  bottom. 

In  operating  the  calorimeter,  the  steam  to  be  tested  enters 
through  the  tube  in  the  top  and  discharges  against  the  bottom 
of  the  perforated  metal  basket.  The  steam,  in  seeking  an 
outlet,  is  forced  to  make  a  sharp  turn  as  it  leaves  the  tube,  thus 
separating  the  moisture  from  it.  The  steam,  which  is  now  dry, 


FIG.  68. — Separating  calorimeter. 

passes  the  sides  of  the  metal  basket  and  through  the  opening 
into  the  outer  chamber.  The  moisture  is  separated  from  the 
steam  and  passes  through  the  perforations  in  the  basket,  collect- 
ing in  the  bottom  of  the  inner  chamber.  The 'amount  of  water 
collected  in  the  inner  chamber  is  indicated  in  a  glass  gage 
located  outside  the  body  of  the  calorimeter  and  connected  at 


120  STEAM  BOILERS 

top  and  bottom  to  the  inner  chamber.  This  gage  is  fitted  with 
a  marker  which  passes  over  a  graduated  scale.  The  scale  is 
usually  graduated  to  read  in  hundredths  of  a  pound. 

The  dry  steam  passes  into  the  outer  chamber  and  out  through 
the  opening  in  the  bottom.  A  gage,  resembling  a  steam  gage,  is 
connected  to  the  outer  chamber  of  the  calorimeter.  The  dial  of 
this  gage  has  two  sets  of  graduations;  the  inner  one  showing  the 
pressure  of  the  steam  in  the  calorimeter  in  pounds  per  square  inch 
above  atmospheric  pressure,  and  the  other  showing  the  weight  of 
steam  flowing  through  the  small  opening  in  the  bottom  during  a 
period  of  10  minutes.  The  gage  is  rather  unreliable  and  for  this 
reason,  it  is  better  to  obtain  the  weight  of  steam  passing  through 
the  calorimeter  by  weighing  it.  This  may  be  done  by  connecting 
a  rubber  tube  to  the  bottom  of  the  calorimeter  and  passing  the 
steam  into  a  tub  or  bucket  of  cold  water,  where  it  will  be  con- 
densed. By  weighing  the  tub  or  bucket  of  water  before  and 
after  passing  the  steam  into  it,  its  increase  in  weight  may  be 
obtained.  This  increase  in  weight  represents  the  weight  of  dry 
steam  that  has  passed  through  the  calorimeter. 

To  obtain  the  quality  of  steam  with  a  separating  calorimeter, 
the  valve  at  the  top  is  opened  wide  and  steam  allowed  to  flow 
through  the  instrument  until  it  becomes  hot.  The  glass  gage  is 
then  drained  through  the  drain  cock  of  any  water  which  it  may 
contain.  After  waiting  a  few  seconds  until  water  again  appears 
in  the  gage  glass,  a  reading  of  the  height  of  the  water  in  the  gage 
glass  is  taken  and  at  the  same  instant  the  end  of  the  rubber  tube 
connected  to  the  bottom  of  the  calorimeter  is  quickly  placed  in  a 
tub  or  bucket  of  water  which  has  previously  been  weighed  and 
placed  near  the  calorimeter.  The  water  and  condensed  steam 
are  collected  in  this  manner  for  10  or  15  minutes,  when  the 
height  of  the  water  in  the  gage  glass  is  again  read  and  at  the 
same  instant  the  end  of  the  rubber  tube  is  removed  from  the  tub 
or  bucket  of  water.  The  weight  of  water  collecting  in  the 
calorimeter  may  then  be  read  from  the  gage  glass  and  the  weight 
of  dry  steam  passing  through  the  calorimeter  obtained  by  weigh- 
ing the  tub  or  bucket  of  water. 

The  calculation  of  quality  of  steam  from  the  readings  taken 
with  a  separating  calorimeter  is  very  simple,  since  the  weight  of 
water  and  of  steam  are  obtained  directly.  If  W  represents 
the  weight  of  water  removed  from  the  steam,  as  indicated  on  the 
glass  gage,  and  W^  represents  the  weight  of  dry  steam  obtained 


ACTUAL  AND  EQUIVALENT '^EVAPORATION    121 

by  condensation  in  a  tub  or  bucket  of  water,  then  the  total 
weight  of  the  wet  steam  is  W  4-  W^  and  the  quality  or  dryness 
will  be 

Wl  W, 

or q 


w+wt        w+w, 

Example :  Suppose  the  glass  gage  shows  that  the  calorimeter 
has  collected  .12  Ib.  of  water  in  a  certain  time,  and  during  the 
same  time  the  tub  of  water  has  increased  in  weight  2  Ib.  4£  oz. 
What  is  the  quality  of  the  steam? 

4J  oz.  =  ^|=  .281  Ib. 

Therefore,  2  Ib.  4J  oz.  =2.281  Ib.  =  W, 
Wj  2.281      ^2.281 


In  this  form  of  calorimeter,  radiation  from  the  outer  walls, 
which  causes  condensation  of  a  portion  of  the  steam,  does  not 
affect  the  accuracy  of  the  results,  as  condensation  can  take 
place  only  in  the  outer  chamber  and  will,  therefore,  affect  only 
steam  from  which  the  moisture  has  already  been  separated. 

The  separating  calorimeter  is  especially  useful  in  determining 
the  quality  of  steam  which  contains  considerable  moisture.  If 
the  quality  of  the  steam  is  so  low  that  one  calorimeter  will  not 
remove  all  the  moisture,  two  calorimeters  may  be  connected  so 
the  first  one  discharges  into  the  second,  thus  forcing  the  steam 
to  pass  through  both.  The  moisture  which  passes  the  first 
calorimeter  will  be  separated  by  the  second.  The  separating 
calorimeter  does  not  give  as  accurate  results  as  the  throttling 
calorimeter  to  be  described  next,  but  it  can  be  used  with  steam 
having  a  lower  quality. 

98.  Throttling  Calorimeter. — The  throttling  calorimeter  oper- 
ates on  an  entirely  different  principle  from  that  of  the  separating 
calorimeter  just  described.  This  form  of  calorimeter  takes  its 
name  from  the  fact  that  the  steam,  whose  quality  is  to  be  deter- 
mined, is  forced  to  pass  through  a  very  small  opening,  thereby 
throttling  it,  or  causing  its  pressure  to  be  reduced. 

Two  forms  of  throttling  calorimeters  are  shown  in  Figs.  69 
and  71.  The  one  shown  in  Fig.  69  is  very  simple  and  is  in  com- 
mon use.  It  consists  of  a  hollow  cylindrical  shell  with  a  ther- 


122 


STEAM  BOILERS 


mometer  well  extending  down  its  center,  and  with  an  opening 
into  the  atmosphere  at  the  bottom.  Steam  is  Jed  into  the 
calorimeter  through  a  sampling  tube  and  valve  and  through  a 
nozzle  which  has  an  opening  of  only  about  .03  of  an  inch  in 
diameter.  An  opening  is  placed  in  the  shell  of  the  calorimeter 
directly  opposite  the  nozzle  and  leading  to  one  branch  of  a 
manometer,  or  glass  "U"  tube  partly  filled  with  mercury  and 
provided  with  a  scale  divided  into  inches. 

The  theory   of   a  throttling   calorimeter  is   as   follows:  The 
steam  drawn  from  the  steam  pipe  by  the  nozzle  is  saturated 


FIG.  69. — Throttling  calorimeter. 


and  under  a,  high  pressure.  Upon  flowing  through  the  nozzle 
into  the  chamber  of  the  calorimeter,  which  is  open  to  the  at- 
mosphere, the  pressure  of  the  steam  will  be  reduced  to  ap- 
proximately atmospheric  pressure.  A  study  of  the  steam 
table  will  show  that  high  pressure  saturated  steam  contains  a 
greater  number  of  heat  units  per  pound  than  low  pressure 
saturated  steam.  The  steam  taken  from  the  steam  pipe  cannot 


ACTUAL  AND  EQUIVALENT  EVAPORATION    123 

gain  any  heat,  since  there  is  no  source  of  heat  present.  Neither 
can  it  lose  heat  except  by  radiation  and,  since  the  calorimeter  is 
small,  the  small  amount  of  heat  lost  in  this  way  may  be  neglected. 
Therefore,  as  far  as  practical  results  are  concerned,  the  steam  in 
the  calorimeter  contains  the  same  number  of  heat  units  per  pound 
as  the  steam  in  the  pipe  from  which  the  sample  is  taken.  Since 
the  low  pressure  steam  in  the  calorimeter  requires  less  heat  to 
saturate  it  than  high  pressure  steam,  there  will  be  more  heat  in 
the  calorimeter  than  is  required  to  saturate  the  steam  after  its 
pressure  has  been  reduced.  As  this  excess  heat  cannot  escape, 
it  is  absorbed  by  the  steam  in  the  calorimeter  thereby  raising- 
its  temperature,  or  superheating  it.  A  numerical  example  will 
make  this  plain.  Suppose  the  steam  in  the  main  pipe  has  a 
pressure  of  150  Ib.  per  sq.  in.  absolute  and  a  quality  of  98  per 
cent.  The  number  of  Blt.u.  per  pound  in  this  steam  will  be 


B.t.u.  = 

=329.6+  .98X861.6 

=  329.6+844.37 
=  1173.97 

and  this  is  the  amount  of  heat  which  enters  the  calorimeter 
per  pound  of  steam.  If  the  steam  inside  the  calorimeter  has  a 
pressure  of  15  Ib.  per  sq.  in.  absolute  and  is  merely  satu- 
rated, it  would  contain  only  1146.9  B.t.u.  per  pound.  Therefore, 
there  will  be  1173.97  —1146.9  =27.07  B.t.u.  inside  the  calorimeter 
in  excess  of  that  required  to  saturate  the  steam  and,  as  this  27.07 
B.t.u.  cannot  escape,  it  is  absorbed  by  the  steam  inside  the 
calorimeter,  thereby  superheating  it. 

The  amount  of  heat  required  to  raise  the  temperature  of  1  Ib. 
of  any  substance  may  be  found  by  multiplying  the  specific  heat 
of  that  substance  by  the  difference  in  temperature  through 
which  the  substance  is  raised.  The  specific  heat  of  superheated 
steam,  when  near  atmospheric  pressure,  is  commonly  taken  as 
0.48,  therefore  the  27.07  B.t.u.  of  excess  heat  mentioned  above 
is  sufficient  to  raise  the  temperature  of  the  steam  in  the  calorim- 
eter an  amount  equal  to  T  in  the  following  formula 

27.07  =  0.48T 
or  T=  ~rTo  =56.4  degrees. 


124  STEAM  BOILERS 

Since  saturated  steam  at  a  pressure  of  15  Ib.  per  sq.  in.  has  a 
temperature  of  213°  F.  the  excess  heat  in  the  calorimeter  is 
sufficient  to  raise  the  temperature  of  the  steam  in  the  calorim- 
eter to  213+56.4  =  269.4°  F.  and,  under  the  conditions  stated 
above,  this  is.  the  temperature  which  a  thermometer  placed  in 
the  well  of  the  calorimeter  would  indicate. 

In  operating  the  throttling  calorimeter,  the  valve  in  the 
sampling  tube  between  the  main  steam  pipe  and  the  calorimeter, 
is  opened  wide  in  order  to  prevent  the  steam  from  being  throttled 
in  passing  through  it. 

The  thermometer  well  should  be  filled  with  a  heavy  oil,  such 
as  cylinder  oil,  and  a  thermometer  capable  of  reading  to  about 
300°  F.  immersed  in  it.  The  manometer  is  filled  about  half  full 
of  mercury,  and  attached  by  a  rubber  tube  to  the  calorimeter. 
The  valve  in  the  manometer  connection  is  opened.  When  the 
calorimeter  has  become  heated  and  the  temperature  as  indicated 
by  the  thermometer  has  become  stationary  the  readings  may  be 
taken. 

The  readings  to  be  taken  for  determining  the  quality  of  the 
steam  are: First,  the  pressure  of  the  steam  in  the  pipe  from  which 
the  sample  is  taken,  for  which  purpose  a  steam  gage  should  be 
attached  to  the  steam  pipe;  second,  the  temperature  inside  the 
calorimeter,  as  indicated  on  the  thermometer  in  the  well;  and 
third,  the  pressure  inside  the  calorimeter  as  indicated  by  the 
manometer.  The  atmospheric  pressure  as  indicated  by  a  barom- 
eter should  also  be  read.  The  readings  of  pressure  and  tempera- 
ture should  be  taken  at  the  same  time. 

The  method  of  calculating  the  quality  is  illustrated  with  the 
following  set  of  readings  as  taken  from  the  calorimeter: 
Gage  pressure  in  steam  pipe  130  Ib.  per  sq.  in. 
Temperature  in  calorimeter  =  249. 25°  F. 
Pressure  in  calorimeter  above  atmospheric  pressure  (manometer 

reading)   =  3  in.  of  mercury  =1.47  Ib.  per  sq.  in. 
Barometer  reading  =28.4  in.  of  mercury  =  13.94  Ib.  per  sq.  in. 
Calculations: 

Absolute  pressure  in  steam  pipe  =  130  + 13.94  =  143.94  Ib.  per  sq.  in. 
Absolute  pressure  in  calorimeter  =  1.47  +  13.94  =  15.41  Ibs. 

per  sq.  in. 

Heat  in  1  Ib.  of  steam  in  pipe  =    h  +  qL,  the  quantities  h  and 
L  being  for  a  pressure  of  143.94  Ib.  per  sq.  in. 


ACTUAL  AND  EQUIVALENT  EVAPORATION    125 
Heat  in  calorimeter    =  H  +  A8(ts  —  t),  in  which 

H  =  ihe  total  heat  in  1  Ib.  of  saturated 
steam  at  the  pressure  which  exists  in 
the  calorimeter. 

ts=  temperature  of  the  superheated  steam  in 
the  calorimeter  as  indicated  by  the 
thermometer. 

£  =  temperature  of  saturated  steam  at  the 
pressure    which  exists  in  the  calorim- 
eter. 
Now  as  shown  before 


H+A8(ts-t)-h 


From  the  observations  and  the  steam  table  we  know  that 

#  =  1147.3 

£s=  249.25 
£  =  214.35 


L  =  863.93 
Therefore, 

_H+AS(t8-t)-h 
q~  ~ 


.3  +  .48(249.25-214.35)  -326.08 
863.93 

1147.3  +  (.48X34.9)  -326.08 

863.93 
1147.3  +  16.75-326.08 

863.93 
007  07 


=96.9  per  cent. 

When  the  throttling  calorimeter  is  used  as  directed  above  and 
results  are  calculated  by  the  method  used  in  the  example,  the 
quality  is  determined  very  accurately.  It  is  not  suitable,  however, 
for  use  with  steam  having  a  quality  less  than  96  per  cent,  as  there 
will  not  then  be  enough  excess  heat  in  the  calorimeter  to  superheat 
the  steam.  Any  one  using  a  throttling  calorimeter  may  know 
when  it  is  not  superheating  the  steam  by  reading  the  thermome- 


126  STEAM  BOILERS 

ter.  If  the  temperature  in  the  calorimeter  is  not  greater  than 
that  corresponding  to  the  temperature  of  saturated  steam  at  the 
pressure  in  the  calorimeter,  then  the  steam  is  not  being  super- 
heated and  the  quality  cannot  be  determined  by  this  method. 
For  example,  if  the  thermometer  had  not  indicated  a  tempera- 
ture higher  than  214.35°  F.  in  the  example  given  above,  it  would 
show  that  the  steam  was  not  being  superheated  and  the  quality 
could  not  have  been  obtained  from  this  data. 

Where  it  is  not  desired  to  obtain  as  accurate  results  as  may  be 
obtained  by  the  method  illustrated  above,  the  manometer 
pressure  may  be  neglected  and  the  pressure  in  the  calorimeter 
assumed  to  be  14.7  Ib.  per  square  inch.  Using  the  data  of  the 
example  above  and  assuming  the  pressure  in  the  calorimeter  to 
be  14.7  Ib.  per  square  inch  the  quality  will  be 

=  1147.3  +  48(249.25-212)  -326.08 
q~  ~~863L93~~ 

=  .971  =  97.1  per  cent 

which  is  a  difference  of  only  .2  per  cent  from  the  result  obtained 
before. 

A  common  method  of  using  the  throttling  calorimeter  is  to 
neglect  both  the  manometer  and  the  barometer  readings,  con- 
sidering the  atmospheric  pressure  and  also  the  pressure  in  the 
calorimeter  to  be  14.7  Ib.  per  square  inch  absolute.  Applying 
this  method  to  the  data  given  above  would  give 

1146.3  +  .48(249.25-212)  -326.7 
<?  =  A863^-  =.97  =  97  per  cent. 

A  chart  for  obtaining  the  quality  by  this  latter  method  is 
shown  in  Fig.  70  and  may  be  used  with  considerable  accuracy  in 
this  locality  (Wisconsin)  because,  while  the  pressure  of  the  at- 
mosphere is  a  little  less  than  14.7  Ib.  per  sq.  in.,  the  pressure 
in  the  calorimeter  will  be  a  little  greater  than  atmospheric  pres- 
sure and  these  two  discrepancies  partially  balance  each  other. 
To  find  the  quality  from  this  chart,  the  gage  pressure  is  located 
on  the  left-hand  side  of  the  chart,  and  the  temperature  inside  the 
calorimeter  is  located  on  the  bottom.  By  following  the  lines 
from  these  points  to  the  point  where  they  meet,  the  quality  may 
be  read  from  the  diagonal  lines.  For  example,  suppose  the 
steam  gage  on  the  pipe  read  15D  Ib.  per  sq.  in.  and  the 
thermometer  read  250°  F.  Following  these  two  points  to  their 
intersection  we  see  the  per  cent  of  moisture  lies  between  3.25 


ACTUAL  AND  EQUIVALENT  EVAPORATION    127 


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128 


STEAM  BOILERS 


per  cent  and  3.50  per  cent  and  is  about  3.35  per  cent,  therefore, 
the  quality  is  100-3.35  =  96.65  per  cent. 

The  form  of  throttling  calorimeter  shown  in  Fig.  71  may  be 
made  from  ordinary  pipe  fittings  and,  if  properly  made,  will 
give  quite  accurate  results.  This  calorimeter  is  made  from  four 
short  nipples,  one  long  nipple,  two  tees,  two  flanges,  one  elbow, 
and  one  union,  put  together  as  shown  in  Fig.  71.  These  fittings 
should  not  be  of  a  less  size  than  1^  in.  in  order  to  prevent 
"wire-drawing"  (throttling)  when  the  steam  is  passing  through. 


FIG.  71. — Throttling  calorimeter  made  from  pipe  fittings. 

A  thin  disc  of  sheet  iron  having  a  small  hole  bored  through  its 
center  is  placed  between  the  two  flanges.  This  hole  is  for  the 
purpose  of  throttling  the  steam  and  thus  superheating  it,  as  is 
done  by  the  nozzle  in  the  throttling  calorimeter  previously 
described.  Each  of  the  tees  is  provided  with  a  thermometer 
well,  as  shown.  The  upper  thermometer  is  intended  to  take  the 
place  of  a  steam  gage  on  the  main  pipe  and  need  not  be  used 
where  a  steam  gage  is  already  on  the  pipe.  By  reading  the 
temperature  on  this  thermometer,  the  corresponding  pressure 
can  be  found  from  a  steam  table.  The  lower  thermometer  shows 
the  temperature  inside  the  calorimeter,  the  same  as  the  ther- 
mometer in  the  other  form  of  throttling  calorimeter. 

Results  are  calculated  by  the  same  method  for  both  calorirn- 


ACTUAL  AND  EQUIVALENT  EVAPORATION    129 

eters,  except  that  in  the  one  shown  in  Fig.  71  no  provision  is 
made  for  measuring  the  pressure  inside  the  calorimeter  and  it 
is  necessary,  therefore,  to  assume  this  pressure  to  be  that  of 
the  atmosphere,  14.7  Ib.  per  sq.  in.  Where  the  pressure  in  the 
calorimeter  is  not  measured,  the  exit  of  steam  from  the  calorim- 
eter should  be  free.  To  accomplish  this  purpose  no  piping  or 
hose  of  any  kind  should  be  attached  to  it  as  this  will  increase  the 
pressure  in  the  calorimeter. 

The  sampling  tube  used  with  calorimeters,  which  is  inserted  in 
the  steam  pipe  where  the  sample  is  to  be  taken,  should  be  of 
1/2-in.  or  3/4-in.  pipe,  threaded  for  a  sufficient  length  to  permit 
screwing  into  the  steam  pipe  until  the  end  of  the  sampling  tube 
comes  within  1/2  in.  of  the  opposite  side  of  the  steam  pipe. 
The  tube  should  have  1/8-in.  holes  bored  in  it,  the  holes  being 
spaced  about  1/2  in.  from  center  to  center,  and  bored  all  around 
the  tube.  None^of  the  holes  should  be  placed  nearer  than  1/2  in. 
to  the  walls  of  the  steam  pipe,  in  order  to  prevent  water  which 
may  be  flowing  along  the  walls  from  entering  the  sampling  tube 
and  giving  a  wrong  value  to  the  quality. 

99.  Superheated  Steam. — If  saturated  steam  is  removed  from 
the  presence  of  water  and  heat  applied  to  it,  its  temperature  may 
be  raised  above  that  at  which  it  was  formed,  and  this  may  be 
done  without  increasing  its  pressure.     When  steam  is  heated 
above  the  boiling  temperature  corresponding  to  its  pressure  it  is 
said  to  be  superheated. 

The  number  of  degrees  by  which  its  actual  temperature  exceeds 
that  of  the  boiling-point  corresponding  to  the  pressure,  is  called  the 
degrees  of  superheat  and  this  term  is  used  to  designate  the  amount 
of  superheat.  Thus,  if  the  gage  pressure  of  the  steam  is  150 
Ib.  per  sq.  in.  and  a  thermometer  inserted  in  it  shows  that 
its  temperature  is  465°,  then,  since  the  temperature  of  saturated 
steam  at  150  Ibs.  per  sq.  in.  pressure  is  about  365°  its  de- 
gree of  superheat  is  465—365  =  100°.  The  temperature  of 
saturated  steam  for  any  pressure  may  be  found  from  the  steam 
table  while  the  actual  temperature  of  superheated  steam  must 
be  measured  with  a  thermometer. 

100.  Total  Heat  of  Superheated  Steam. — Superheated  steam 
contains  more  heat  per  pound  than  saturated  steam  at  the  same 
pressure.     The  total  heat  above  32°  F.  contained  in  a  pound  of 
superheated  steam  may  be  found  by  adding  to  the  total  heat  of 
saturated  steam  for  the  same  pressure,  as  found  in  the  steam 

12 


130 


STEAM  BOILERS 


tables,  the  number  of  heat  units  required  to  superheat  the  steam. 
The  method  formerly  used  for  calculating  the  number  of  heat 
units  required  to  superheat  a  pound  of  steam  was  to  multiply 
the  specific  heat  of  superheated  steam  by  the  degrees  of  superheat. 
Recent  investigation  shows  that  the  specific  heat  of  superheated 
steam  is  different  at  different  temperatures, "  therefore  this 
method  of  determining  the  number  of  heat  units  required  to 
superheat  steam  is  liable  to  cause  serious  error  unless  the  average 
specific  heat  can  be  determined. 

Within  recent  years  many  experiments  have  been  made  to 
determine  the  number  of  heat  units  required  to  superheat  steam. 
The  results  of  these  experiments  are  shown  in  the  following 
table.  The  total  heat  contained  in  a  pound  of  superheated 
steam  may  be  found  by  adding  the  values  given  in  this  table  to 
the  total  heat  of  dry  saturated  steam  as  found  in  a  steam  table. 

HEAT  UNITS  REQUIRED  TO  SUPERHEAT  STEAM 


Degrees  of  superheat 

Absolute 

pressure 

10 

20 

40 

60 

80 

100 

130 

160 

200 

250 

300 

1 

4.9 

9.6 

18.8 

27.9 

36.9 

46.0 

59.6 

73.2 

91.3 

114.0 

136.8 

10 

5.4 

10.4 

20.1 

29.6 

39.0 

48.4 

62.4 

76.3 

94.9 

118.0 

141.2 

15 

5.5 

10.6 

20.5 

30.2 

39.7 

49.2 

63.3 

77.4 

96.1 

119.4 

142.9 

20 

5.6 

10.8 

20.9 

30.7 

40.3 

49.9 

64.1 

78.3 

97.1 

120.6 

144.2 

30 

5.7 

11.1 

21.4 

31.4 

41.3 

51.0 

65.5 

79.8 

98.8 

122.6 

146.5 

40 

5.9 

11.3 

21.8 

32.0 

42.0 

51.9 

66.6 

81.1 

100.3 

124.2 

148.3 

50 

6.0 

11.5 

22.2 

32.5 

42.4 

52.6 

67.4 

82.1 

101.4 

125.6 

149.8 

60 

6.0 

11.7 

22.5 

32.9 

43.2 

53.3 

68.2 

82.9 

102.4 

126.7 

151.0 

80 

6.2 

11.9 

22.9 

33.6 

44.0 

54.2 

69.3 

84.2 

103.9 

128.4 

152.9 

100 

6.3 

12.2 

23.3 

34.1 

44.6 

55.0 

70.2 

85.2 

105.1 

129.7 

154.4 

130 

6.4 

12.4 

23.8 

34.7 

45.4 

55.8 

71.3 

86.4 

106.4 

131.2 

156.1 

160 

6.5 

12.6 

24.2 

35.3 

46.0 

56.6 

72.1 

87.4 

107.5 

132.5 

157.5 

200 

6.7 

12.9 

24.7 

35.9 

46.8 

57.4 

73.1 

88.6 

108,9 

134.1 

159.3 

250 

6.9 

13.2 

25.1 

36.5 

47.6 

58.4 

74.3 

89.9 

110.4 

135.9 

161.3 

300 

7.0 

13.5 

25.6 

37.1 

48.3 

59.2 

75.3 

91.0 

111.7 

137.4 

163.0 

The  use  of  this  table  may  be  illustrated  by  the  following 
example. 

Example :  Determine  the  number  of  heat  units  contained  in  a 
pound  of  superheated  steam  having  a  pressure  of  130  Ib.  per 
sq.  in.  absolute  and  having  a  temperature  of  447.1°  F. 

By  referring  to  the  steam  table,  we  see  that  the  temperature 
of  saturated  steam  at  130  Ib.  pressure  is  347.1°  and  that  its  total 
heat  is  1187.8  B.t.u.  The  degrees  of  superheat  are,  therefore, 
447.1-347.1  =  100°  and  the  above  table  shows  that  for  this 


ACTUAL  AND  EQUIVALENT  EVAPORATION    131 

degree  of  superheat  and  for  a  pressure  of  130  Ib.  the  number 
of  heat  units  required  to  superheat  the  steam  is  55.8.  The 
pound  of  superheated  steam  will,  therefore,  contain 

1187.8  +  55.8  =  1243.6  B.t.u. 

The  average  specific  heat  of  the  superheated  steam  may  be 
found  from  the  table  by  dividing  the  value  given  in  the  table  by 
the  degrees  of  superheat.  Thus,  for  the  above  example  the 
average  specific  heat  would  be 


Since  superheated  steam  contains  more  heat  than  dry  saturated 
steam  it  is  evident  that  the  superheated  steam  is  also  dry.  If 
superheated  steam  is  passed  through  a  throttling  calorimeter, 
it  will  show  a  quality  greater  than  100  per  cent,  which  indicates 
simply  that  the  steam  was  already  superheated  when  it  entered 
the  calorimeter. 

101.  Density  of  Superheated  Steam.  —  The  weight  per  cubic 
foot  of  superheated  steam,  or  its  density,  may  be  calculated  from 
the  following  equation: 

JL1684£ 
M-461 
in  which  D  is  the  weight  per  cubic  foot, 

p  is  the  absolute  pressure  in  pounds  per  square  inch, 
and  ts  is  the  temperature  of  the  steam  in  degrees  Fahrenheit. 
The  temperature  ts  in  the  above  formula  may  be  found  by 
adding  the  number  of  degrees  of  superheat  to  the  temperature  of 
saturated  steam  corresponding  to  the  pressure  p  as  found  from 
the  steam  table. 

Example  :  What  is  the  weight  per  cubic  foot  of  superheated 
steam  having  a  pressure  of  120  Ib.  per  sq.  in.  absolute  and 
59  degrees  of  superheat? 

Since  the  temperature  of  saturated  steam  at  120  Ib.  per  sq.  in. 
is  341°  F., 

$,=341+59  =  400 

1.684X120, 
"  400+461   ~M 

102.  Superheaters.  —  Steam  may  be  superheated  by  taking  it 
away  from  the  presence  of  water  and  applying  heat  to  it.     If 
the  steam  is  wet  to  begin  with,  the  heat  will  first  dry  the  steam 
and  then  superheat  it.     There  are  three  methods  in  use  for  super- 


132  STEAM  BOILERS 

heating  steam.  The  first  and  most  economical  of  these  methods 
is  to  pass  the  saturated  steam  through  coils  of  pipe  placed  in  the 
path  of  the  hot  flue  gases  on  their  way  from  the  boiler  to  the 
chimney.  Unless  the  steam  has  a  very  high  pressure,  about  100° 
of  superheat  may  be  obtained  in  this  way  from  heat  which  would 
otherwise  pass  out  the  chimney  and  be  wasted.  This  method 
can  be  used  only  where  the  draft  will  not  be  seriously  impaired 
by  lowering  the  temperature  of  the  flue  gases. 

The  second  method  consists  in  placing  the  superheater  inside 
the  boiler  setting,  allowing  the  hot  gases  to  pass  through  it 
before  they  leave  the  boiler  and  in  some  cases  even  before  they 
strike  the  boiler.  This  method  has  the  disadvantage  that 
the  temperature  is  rather  hard  to  regulate,  but  it  is  quite 
economical. 

The  third  method  of  superheating  steam  is  to  have  the  super- 
heater entirely  independent  of  the  boiler  and  separately  fired. 
With  this  method  the  temperature  may  be  easily  regulated  and 
the  superheater  readily  cut  out  when  required,  but  it  is  more 
wasteful  of  fuel  than  either  of  the  other  two  methods. 

103.  The    Future    of    Superheated    Steam.— It    appears    that 
superheating  will  continue  to  grow  in  favor,  but  the  degree  of 
superheat  will  be  moderate  and  the  devices  used  for  securing 
the  superheat  will  be  those  which  are  placed  in  the  combustion 
chamber  of  the  boiler  or  those  made  to  utilize  the  waste  heat  in 
the  chimney  gases.     One  of  the  principal  wastes  in  a  steam  plant 
comes  from  the  heat  lost  up  the  chimney  and  any  of  this  heat 
that  is  saved  is  a  direct  gain.     The  temperature  in  chimneys  is 
from  150°  to  300°   above  the  temperature  of  the  steam  in  the 
boiler  and  is  often  much  higher  than  is  necessary  to  produce 
sufficient  draft,  so  that  a  part  of  this  heat  may  be  used  for 
superheating  the  steam  without  any  evil  effects  in  the  running 
of  the  plant,  and  without  any  extra  cost  for  fuel.     The  saving 
thus  effected  may  amount  to  from  5  to  15  per  cent  according 
to  the  design  and  size  of  the  boilers.     Often  boilers  that  will 
barely  furnish  enough  steam  for  the  engines  may  be  made  to 
meet  the  requirements  easily  by  the  addition  of  a  superheater 
in  the  chimney  flue. 

104.  Equivalent  Evaporation. — If  we  wish  to   compare  the 
amounts  of  steam  generated  by  boilers  which  are  working  under 
different  conditions  it  is  necessary  to  have  some  standard  with 
which  to  compare  them.     Thus,  one  boiler  may  be  receiving 


ACTUAL  AND  EQUIVALENT  EVAPORATION     133 

feed  water  at  60°  F.  and  generating  steam  at  a  pressure  of  120 
Ib.  per  sq.  in.  gage,  having  a  quality  of  96  per  cent;  under  these 
conditions  this  boiler  generates  8  Ib.  of  steam  per  pound  of 
coal.  Another  boiler  taking  feed  water  at  170°  F.  and  generating 
steam  at  a  pressure  of  150  Ib.  per  sq.  in.  gage,  having  a 
quality  of  98  per  cent,  produces  7^  Ib.  of  steam  per  pound  of 
coal  under  these  conditions.  By  simply  comparing  the  number 
of  pounds  of  steam  generated  per  pound  of  coal  in  each  case,  no 
idea  can  be  gained  of  which  boiler  is  doing  more  work.  It 
is  necessary  to  have  some  standard  by  which  to  compare  the 
performance  of  each  boiler. 

If  we  wish  to  compare  two  different  lengths,  we  first  compare 
each  of  them  to  some  standard  length,  such  as  the  foot  or  the 
yard.  Thus  one  length,  when  compared  to  the  standard,  may  be 
three  times  as  long,  while  another  length,  compared  to  the  same 
standard,  may  be  six  times  as  long  as  the  standard,  showing  that 
the  second  distance  is  twice  as  great  as  the  first. 

In  comparing  the  performance  of  boilers  we  take  as  the 
standard  the  number  of  heat  units  transferred  when  one  pound 
of  feed  water  having  a  temperature  of  212°  F.  is  turned  into 
steam  having  a  temperature  of  212°  F.  or  a  pressure  of  14.7  Ib. 
per  sq.  in.  absolute.  This  requires  only  the  latent  heat  of  steam 
at  14.7  Ib.  per  sq.  in.  absolute  to  be  transferred,  which,  from  the 
steam  table,  is  965.8  B.t.u. 

As  an  example  of  the  way  in  which  we  may  compare  the 
performance  of  a  boiler  with  this  standard,  suppose  that  6  Ib.  of 
feed  water  are  pumped  into  a  boiler  for  every  pound  of  coal 
burned,  the  feed  water  having  a  temperature  of  32°  F.  and  the 
steam  being  formed  under  a  pressure  of  125  Ib.  per  sq.  in.  ab- 
solute and  having  a  quality  of  100  per  cent.  Referring  to  the 
steam  table  we  see  that  each  pound  of  steam  formed  under  these 
conditions  receives  1186.9  B.t.u.  and  the  6  Ib.  receives  6x1186.9 
=  7121.4  B.t.u.  This  is  equivalent  to  7121.4-^965.8  =  7.37  Ib.  of 
steam  formed  from  feed  water  at  212°  into  steam  at  212°. 
Suppose  the  feed  water  in  this  example  had  a  temperature  of 
150°  instead  of  32°,  the  heat  it  would  receive  would  then  be 
H—  (£  —  32)  per  pound  or  the  6  Ib.  would  receive 

Q[H-  (£-32)]  =  6[1186.9-  (150-32)] 
=  6(1186.9-118) 
=  6X1068.9  =  6413.4  B.t.u. 


134  STEAM  BOILERS 

The  term  (t  —  32)  represents  the  heat  in  the  feed  water  above  32°. 
The  6  Ib.  of  water  evaporated  under  the  above  conditions  would 
be  equivalent  to  6413.4-^-965.8  =  6.64  Ib.  evaporated  from  a  feed 
water  temperature  of  212°  into  steam  at  212°.  As  a  further 
condition,  suppose  the  steam  formed  in  the  last  example  had  a 
quality  of  98  per  cent,  the  feed  water  being  at  150°.  In  this  case 
the  heat  given  to  each  pound  of  steam  would  be 

h  +  qL-(t-32) 

=  315  +  .98X871.9-  (150-32) 
=  315  +  854.5-118 
=  1051.5  B.t.u. 

and  for  the  6  Ib.,  6X1051.5  =  6309  B.t.u.  and  this  would  be 
equivalent  to  6309-^965.8  =  6.53  Ib.  evaporated  from  feed  water 
at  212°  into  steam  having  a  temperature  of  212°. 

In  the  three  cases  given  above  the  7.37,  6.64  or  6.53  Ib.  is 
called  the  equivalent  evaporation.  This  quantity  is  sometimes 
called,  also,  the  equivalent  evaporation  from  and  at  212°  or  the 
evaporation/row  and  at.  We  may  define  the  equivalent  evapora- 
tion as  the  total  number  of  heat  units  supplied  to  a  quantity 
of  steam  divided  by  the  latent  heat  of  steam  at  a  pressure  of  14.7 
Ib.  per  sq.  in.  absolute. 

105.  Factor  of  Evaporation. — The  equivalent  evaporation  of 
1  Ib.  of  steam  is  called  the  Factor  of  Evaporation.  In  the  last 

example  given  above,  the  factor  of  evaporation  would  be  ng.  '   = 

ybo.o 

1.088  +  .  If  we  multiply  the  actual  evaporation  ,by  the  factor 
of  evaporation  the  result  will  be  the  equivalent  evaporation. 
Thus,  6  Ib.  of  water  evaporated  under  the  conditions  given  in  the 
last  example  above  would  be  equivalent  to  6x1.088  =  6.53  Ib. 
evaporated  from  and  at  212°,  which  is  the  same  result  as  ob- 
tained by  the  other  method  of  calculation.  The  factor  of 
evaporation  may  be  calculated  with  the  following  formula: 

h+qL-(t-32) 

965.8 
in  which,  /  =the  factor  of  evaporation 

h  =  the  heat  of  the  liquid  for  the    boiler    pressure 
L  =  the  latent  heat  of  the  steam  at  the  boiler  pressure 
q  =  the  quality  of  the  steam 
and  t  =  the  temperature  of  the  feed  water. 

The  following  table  gives  the  factors  of  evaporation  for  various 


ACTUAL  AND  EQUIVALENT  EVAPORATION    135 

FACTORS  OF  EQUIVALENT  EVAPORATION 


Steam 
pressure 
by  gage 

Temperature  of  feed  water  in.  degrees  F. 

Steam 
pressure 
by  gage 

40 

50 

60 

70 

80 

90 

100 

110 

120 

10 

1.188 

1.177 

1.167 

1.157 

1.146 

.136 

1.125 

1.115 

1.105 

10 

20 

1.194 

1.183 

1.173 

1.163 

1.152 

.142 

1.132 

1.121 

1.111 

20 

30 

1.199 

1.188 

1.178 

1.168 

1.157 

.147 

1.136 

1.126 

1.116 

30 

40 

1.203 

1.192 

1.182 

1.172 

1.161 

.151 

1.140 

1.130 

1.120 

40 

50 

1.206 

.196 

1.185 

1.175 

1.165 

.154 

1.144 

1.133 

1.123 

50 

60 

1.209 

.199 

1.188 

1.178 

.168 

.157 

1.147 

1.136 

1.126 

60 

70 

1.212 

.201 

1.191 

1.181 

.170 

1.160 

.150 

1.139 

1.129 

70 

80     • 

1.214 

.204 

1.194 

1.183 

.173 

1.162 

.152 

1.142 

.131 

80 

90 

1.217 

.206 

1.196 

1.186 

.175 

1.165 

.154 

1.144 

.134 

90 

100 

1.219 

.208 

1.198 

1.188 

.177 

1.167 

.157 

1.146 

.136 

100 

110 

1.221 

.210 

1.200 

1.190 

.179 

1.169 

.158 

1.148 

.138 

110 

120 

1.223 

.212 

1.202 

1.191 

1.181 

1.171 

.160 

1.150 

.140 

120 

130 

1.224 

.214 

1.204 

1.193 

1.183 

1.173 

.162 

1.152 

.141 

130 

140 

1.226 

.216 

1.205 

1.195 

1.185 

1.174 

.164 

1.153 

.143 

140 

150 

1.228 

.217 

1.207 

1.196 

1.186 

1.176 

.165 

1.155 

1.145 

150 

160 

1.229 

.219 

1.208 

.198 

1.188 

1.177 

.167 

1.156 

1.146 

160 

170 

1.231 

.220 

1.210 

.199 

1.189 

1.179 

.168 

1.158 

1.148 

170 

200 

1.235 

.224 

1.214 

.203 

1.193 

1.183 

.172 

1.162 

1.152 

200 

225 

1.238 

.227 

1.217 

.206 

1.196 

1.186 

1.175 

1.165 

1.155 

225 

250 

1.240 

.230 

1.220 

.209 

1.199 

1.188 

1.178 

1.168 

1.157 

250 

275 

1.243 

.233 

1.222 

.212 

1.201 

1.191 

1.181 

1.170 

1.160 

275 

300 

1.245 

.235 

1.225 

.214 

1.204 

1.193 

1.183 

1.173 

1.162 

300 

FACTORS  OF  EQUIVALENT  EVAPORATION— Continued 


Steam 
pressure 
by  gage 

Temperature  of  feed  water  in  degrees  F. 

Steam 
pressure 
by  gage 

130 

140 

150 

160 

170 

180 

190 

200 

210 

212 

10 

1.094 

1.084 

1.073 

1.063 

1.053 

1.042 

1.032 

.021 

1.011 

.009 

10 

20 

1.100 

1.090 

.080 

1.069 

1.059 

1.048 

1.038 

.027 

1.017 

.015 

20 

30 

1.105 

1.095 

.084 

1.074 

1.064 

.053 

1.043 

.032 

1.022 

.020 

30 

40 

1.109 

1.099 

.088 

1.078 

1.068 

.057 

.047 

.036 

1.026 

.024 

40 

50 

1.113 

1.102 

.092 

1.081 

1.071 

.061 

.050 

.040 

1.029 

.027 

50 

60 

1.116 

1.105 

.095 

1.084 

1.074 

.064 

.053 

1.043 

1.032 

.030 

60 

70 

1.118 

1.108 

.098 

1.087 

1.077 

.066 

.056 

1.045 

1.035 

.033 

70 

80 

1.121 

1.111 

.100 

1.090 

1.079 

.069 

.058 

1.048 

1.037 

.035 

80 

90 

1.123 

1.113 

.102 

1.092 

1.082 

.071 

.061 

1.050 

.040 

.038 

90 

100 

1.125 

1.115 

.105 

1.094 

1.084 

1.073 

.063 

1.052 

.042 

.040 

100 

110 

1.127 

1.117 

.106 

1.096 

1.086 

1.075 

.065 

1.054 

.044 

.042 

110 

120 

1.129 

1.119 

.108 

1.098 

1.087 

1.077 

.067 

1.056 

.046 

1.044 

120 

130 

1.131 

.121 

.110 

1.100 

1.089 

1.079 

.068 

1.058 

.047 

1.045 

130 

140 

1.133 

.122 

.112 

1.101 

1.091 

1.080 

.070 

1.060 

.049 

1.047 

140 

150 

1.134 

.124 

.113 

1.103 

1.092 

1.082 

.072 

1.061 

.051 

1.049 

150 

160 

1.136 

.125 

.115 

1.104 

1.094 

1.083 

.073 

1.063 

.052 

1.050 

160 

170 

1.137 

.127 

.116 

1.106 

1.095 

1.085 

.075 

1.064 

.054 

1.051 

170 

200 

1.141 

.131 

1.120 

1.110 

1.099 

1.089 

.079 

1.068 

.058 

1.055 

200 

225 

1.144 

.134 

1.123 

1.113 

1.102 

1.092 

.082 

1.071 

.061 

1.058 

225 

250 

1.147 

.136 

1.126 

1.116 

1.105 

1.095 

.084 

1.074 

.063 

1.061 

250 

275 

1.149 

1.139 

1.129 

1.118 

1.108 

1.097 

.087 

1.076 

.066 

1.064 

275 

300 

1.152 

1.141 

1.131 

1.121 

1.110 

1.100 

.089 

1.078 

.068 

1.066 

300 

136  STEAM  BOILERS 

pressures  and  feed-water  temperatures.  In  calculating  the 
quantities  given  in  this  table  the  quality  of  the  steam  has  been 
neglected,  it  being  assumed  that  the  steam  is  perfectly  dry. 
The  pressures  given  in  the  table  are  gage  pressures. 

106.  Boiler  Horse-power. — In  a  previous  assignment  the  boiler 
horse-power  was  denned  in  terms  of  the  number  of  square  feet  of 
heating  surface.  This  is  a  very  unsatisfactory  way  of  rating  a 
boiler  as  all  parts  of  the  heating  surface  of  a  boiler  are  not  equally 
effective  in  transmitting  heat,  that  which  is  near  the  furnace 
transmitting  more  than  the  part  near  the  smoke  outlet. 

Since  the  work  of  a  boiler  consists  in  evaporating  water,  the 
logical  basis  for  rating  it  is  on  the  number  of  pounds  of  water 
evaporated,  but  as  the  conditions  under  which  the  water  is 
evaporated  are  different  in  different  boilers,  the  evaporation 
should  be  reduced  to  some  standard,  such  as  the  equivalent 
evaporation. 

The  best  and  most  commonly  used  definition  of  a  boiler  h.p. 
is  as  follows:  One  boiler  h.p.  is  the  evaporation  of  34^  Ib.  of 
water  per  hour  from  a  temperature  of  212°  into  steam  at  212°. 
This  may  be  expressed  in  few  words  by  saying  that  a  boiler  h.p. 
is  the  equivalent  evaporation  of  34£  Ib.  of  water.  To  illus- 
trate this  by  an  example,  suppose  we  wish  to  find  the  horse- 
power of  a  boiler  which  evaporates  12,000  Ib.  of  feed  water  per 
hour  from  a  feed-water  temperature  of  170°  into  steam  at  150  Ib. 
gage  pressure.  Referring  to  the  table  of  factors  of  evaporation 
we  see  that  for  feed  water  of  170°  and  steam  at  150  Ib.  gage 
pressure  the  factor  of  evaporation  is  1.092.  Therefore,  12,000  Ib. 
is  equivalent  to  12,000X1.092  =  13,104  Ib.  from  and  at  212°. 
The  boiler  h.p.  would  then  be 

Boiler  h.     .  =  A4 


CHAPTER  IX 
FUELS 

107.  Classification  of  Fuels. — Fuels  may  be  defined  as  those 
substances  which  may  be  burned  economically  by  means  of  air, 
to  generate  heat.     The  chief  heat  producing  elements  of  all  fuels 
are  carbon  and  hydrogen.     Fuels  may  be  classed  as  artificial  and 
natural. 

Artificial  fuels  are  those  which  are  manufactured  and  which 
are  not  usually  found  in  nature,  at  least  in  a  form  suitable  for 
use  in  a  furnace.  They  are  generally  manufactured  from  natural 
fuels,  or  they  are  the  by-products  of  some  process  of  manufacture. 

Natural  fuels  are  those  forms  of  carbon  and  hydrogen  which 
are  found  in  nature  in  a  condition  to  be  used.  These  include 
wood,  coal,  mineral  oil,  and  natural  gas.  The  solid  fuels  may  be 
classified  as  wood,  peat,  and  coal;  arid  coal  is  further  divided 
into  several  classes  as  will  be  seen  later. 

108.  Wood. — Wood  as  a  fuel  is  rapidly  dropping  out  of  use, 
though  it  is  still  important  in  some  of  the  more  thinly  settled 
sections  of  the  country,   and  around  wood-working  establish- 
ments where  the  refuse  is  burned.     When  freshly  cut,  wood 
contains  about  50  per  cent  of  moisture  but  when  air  dried,  con- 
tains only  about  20  per  cent  moisture,  and  in  this  condition  it 
has  a  heating  value  of  about  5800  B.t.u.  per  pound. 

The  composition  of  woods  of  different  kinds  is  practically  the 
same,  the  average  being  about  as  follows:  carbon,  49.70  per  cent; 
hydrogen,  6.06  per  cent;  oxygen,  41.30  per  cent;  nitrogen,  1.05 
per  cent;  ash,  1.89  per  cent. 

109.  Peat. — Peat  lies  between  wood  and  coal  in  its  character, 
and,  in  fact,  seems  to  be  coal  in  the  process  of  formation.     It 
occurs  in  certain  swampy  regions  in  the  temperate  zone  and  is 
composed  of  semi-aquatic  plants  which,  under  special  conditions 
of  heat  and  moisture,  are  going  through  a  transformation  whereby 
the  oxygen  is  being  eliminated  and  the  carbon  left  behind.     It 
occurs  in  beds  from  1  to  40  ft.  thick;  that  near  the  surface,  being 
in  a  less  decomposed  state,  is  light,  spongy,  and  of  a  fibrous 
nature  and  of  a  yellow  or  reddish-brown  color.     Lower  down  it 

13  137 


138  STEAM  BOILERS 

is  of  a  darker  color  and  is  more  compact,  while  in  the  still  lower 
layers  it  is  almost  black  and  of  a  pitchy  nature. 

In  its  natural  state,  peat  contains  too  much  water  to  be  used 
as  a  fuel,  the  water  sometimes  being  as  high  as  85  or  90  per  cent 
of  its  entire  weight,  and  it  must  be  dried  out  before  it  can  be  used. 
Owing  to  the  abundance  of  other  good  fuels  in  this  country, 
peat  is  not  used  very  much,  but  in  Ireland,  Germany,  and  Sweden 
it  is  used  extensively. 

The  average  composition  of  perfectly  dry  Irish  peat  is  about 
as  follows:  carbon,  59.00  per  cent;  hydrogen,  6.00  per  cent; 
oxygen,  30.00  per  cent;  nitrogen,  1.25  per  cent;  ash,  4.00  per- 
cent. In  this  condition  its  heating  value  per  pound  is  10,040 
B.t.u. 

110.  Coal. — Coal  is  the  most  important  and  most  commonly 
used  fuel  which  we  have.  This  is  because  it  is  found  scattered 
over  such  widely  distributed  areas  and  in  such  large  quantities; 
because  it  has  a  high  heating  value  for  a  given  weight;  and 
because  it  is  easily  transported  from  place  to  place  and  stored. 
Coal  represents  the  energy  stored  in  the  earth  during  past  ages 
by  the  sun,  whose  heat  aided  the  formation  of  the  coal. 

Coal  is  a  fossilized  product  of  plant  growth  which  has  accumu- 
lated during  past  ages.  Its  origin  is  explained  as  follows: 
In  the  early  ages  of  the  earth  the  atmosphere  contained  a  very 
large  proportion  of  carbon  dioxide,  much  more  than  it  does  at 
present.  This  excess  of  carbon  in  the  air,  which  is  the  food  upon 
which  plants  live,  caused  the  earth  to  be  covered  with  a  very 
dense  and  rank  growth  of  vegetation.  By  the  continual  growth 
and  death  of  this  vegetation,  parts  of  the  earth  became  covered 
with  vegetable  matter,  which,  as  time  went  by,  was  buried  under 
a  mass  of  soil  and  rocks.  The  pressure  of  this  weight,  together 
with  the  heat  from  the  sun  caused  a  gradual  change  in  the 
structure  of  the  vegetable  matter  whereby  some  of  its  oxygen 
was  liberated  and  the  remainder  assumed  the  form  of  coal.  As 
this  process  is  a  very  gradual  one,  we  would  expect  to  find  the 
vegetable  matter  in  all  stages  of  transformation,  varying  from 
the  vegetable  form  to  solid  coal.  These  stages  extend  all 
through  the  various  grades  of  peat,  lignite,  bituminous  or  soft 
coal,  and  anthracite  or  hard  coal,  the  anthracite  being  the 
furthest  along  in  the  development  of  the  coal,  having  less  oxygen, 
more  carbon,  and  being  heavier  and  more  homogeneous. 

The  following  table  shows  very  well  the  change  in  the  principal 


FUELS 


139 


constituents  of  the  coal  in  the  process  of  change  from  wood  to 
anthracite  coal,  the  values  being  only  approximate.  The  ash 
and  other  elements  besides  those  given  here  have  been  left  out 
in  giving  the  percentages. 


Description 

Carbon 

. 
Hydrogen 

Oxygen 

Wood  fiber 

52% 

5  5% 

42  5% 

Peat  
Lignite               .    . 

60 
70 

5.9 
5  3 

34.1 

27  7 

Bituminous  coal  
Semi-bituminous  coal 

76 

88 

5.7 
5  1 

18.3 
6  9 

Anthracite  coal  

92 

3  9 

4  1 

The  most  noticeable  change  is  in  the  carbon,  which  increases, 
and  in  the  oxygen,  which  decreases,  as  the  coal  is  developed  from 
wood  into  the  harder  varieties  of  coal. 

As  the  process  of  change  from  wood  into  coal  is  a  very  gradual 
one,  no  sharp  line  of  distinction  can  be  drawn  between  the 
different  classes  of  coal,  but  they  may  be  classified  in  a  general 
way  according  to  the  amounts  of  fixed  carbon  and  volatile 
matter  which  they  contain.  The  following  is  suggested  as  such  a 
classification: 

Per  cent  of  volatile  matter  in  the 
combustible  part  of  the  coal 

Anthracite 0      to    7.5 

Semi-anthracite 7 . 5  to  12 . 5 

Semi-bituminous 12 . 5  to  25 

Bituminous 25      to  40 

Lignite over       40 

Bituminous  coal  may  be  further  classified  into  Caking,   Non- 
caking,  and  Cannel  coals. 

While  coal  is  widely  scattered  over  the  United  States,  the 
different  varieties  are  confined  more  or  less  to  certain  localities 
as  indicated  in  the  following  classification. 

Eastern     portions    of    Allegheny    Mountains    and 

Rocky  Mountains  of  Colorado. 
f  Caking — Mississippi  Valley. 

Bituminous   >  Non-caking  —  Maryland,     Virginia,    and    Pennsyl- 
5'  ]       vania. 

[  Cannel — Pennsylvania,  Indiana,  and  Missouri. 
Lignites Colorado,  Kentucky,  Southwest,  and  Northwest. 


Anthracite. . 


140  STEAM  BOILERS 

The  characteristics  of  each  of  the  varieties  of  coal  will  next  be 
considered,  starting  with  the  softer  varieties. 

111.  Lignite. — This  substance  lies  between  peat  and  bitumi- 
nous coal,  and  is  supposed  to  be  of  later  origin  than  bituminous 
coal.  It  varies  in  color  from  brown  to  almost  black,  that  coming 
from  a  greater  depth  being  darker  than  that  obtained  near  the 
surface.  Some  lignites  show  the  vegetable  structure  quite 
plainly  while  others  are  quite  dense.  As  lignite  is  quite  soft  and 
brittle,  it  is  not  suitable  for  transportation  and  must,  therefore, 
be  used  near  the  place  where  mined.  This  restricts  its  use  con- 
siderably. If  exposed  to  the  weather  for  any  length  of  time  the 
softer  varieties  crumble  and  absorb  moisture;  they  must,  there- 
fore, be  used  soon  after  being  mined.  It  has  but  moderate 
heating  value,  but  is  used  to  some  extent  in  parts  of  the  West 
where  it  is  plentiful,  and  where  other  varieties  of  coal  are  expen- 
sive. Its  average  composition  when  dry  is  about  as  follows: 
fixed  carbon,  44.7  per  cent;  volatile  matter,  54.92  per  cent; 
ash,  6.41  per  cent. 

It  will  be  noticed  that  the  analysis  just  given  is  expressed  in 
different  terms  than  those  previously  given.  This  analysis  is 
called  a  proximate  analysis  while  those  given  previously  are 
called  ultimate  analyses.  In  the  ultimate  analysis  each  con- 
stituent in  the  fuel  is  determined  and  its  amount  found.  While 
these  elements  do  exist  in  the  fuel,  most  of  them  are  combined 
with  other  substances;  thus,  part  of  the  hydrogen  is  combined 
with  different  proportions  of  carbon,  forming  a  whole  series  of 
substances,  such  as  marsh  gas,  olefiant  gas,  etc.,  which  are  very 
volatile,  that  is,  they  are  readily  driven  out  of  the  fuel  by  heating 
it.  The  remainder  of  the  hydrogen  may  be  combined  with 
oxygen  in  the  form  of  water. 

All  of-  the  carbon  which  is  not  combined  with  other  substances 
is  called  fixed  carbon  because  it  exists  as  carbon  and  cannot  be 
driven  out  of  the  fuel  by  a  low  degree  of  heat. 

We  see  from  the  above  that  fuels  contain  volatile  substances 
and  nonvolatile  or  fixed  substances,  and  the  proximate  analysis 
shows  the  relative  amounts  of  these.  When  coal  is  heated  away 
from  air  (so  it  will  not  burn)  the  volatile  matter  is  driven  off  and 
a  coke  is  left.  This  coke  contains  the  fixed  carbon  and  the  ash. 

It  must  be  remembered  that  the  fixed  carbon  shown  by  a 
proximate  analysis  does  not  represent  all  of  the  carbon  in  the  fuel. 
A  certain  kind  of  coal  may  contain  as  much  as  80  per  cent  carbon, 


FUELS  141 

yet  have  only  50  per  cent  of  fixed  carbon,  the  other  30  per  cent 
being  combined  with  hydrogen  in  the  form  of  volatile  matter. 

112.  Bituminous  Coal. — The  classification  of  bituminous  coal 
is  made  difficult  by  the  lack  of  sharp  lines  of  distinction  between 
the  different  varieties.     In  ultimate  composition  it  consists  of: 
carbon,  75  to  80  per  cent;  hydrogen,  5  to  6  per  cent;  nitrogen, 
1  to  2  per  cent;  oxygen,  4  to  20  per  cent;  sulphur,  0.4  to  3  per 
cent;  ash,  3  to  12  per  cent. 

The  principal  characteristic  of  this  coal  is  that  it  emits  yellow 
flame  and  smoke  when  burning.  In  color  it  varies  from  pitch 
black  to  brown,  with  a  resinous  luster  in  the  denser  varieties 
and  a  silky  luster  in  the  less  compact  specimens.  All  bituminous 
coals  may  be  roughly  divided  into  caking  and  non-caking. 

113.  Caking  Coal. — This  is  the  name  given  to  those  coals 
which,  when  thrown  on  the  fire,  seem  to  melt  and  run  together. 
This  fused  mass  of  coal  sometimes  spreads  entirely  over  the  fire 
and  seems  to  swell  in  size  and  form  blisters  in  spots,  these 
blisters  bursting  and  emitting  streams  of  gas  which  burn  with  a 
bright  yellow  or  reddish  flame  terminating  in  smoke.     These 
coals  are  usually  very  rich  in  volatile  hydrocarbons  and  are, 
therefore,  well  adapted  to  gas  making. 

114.  Non-caking  Coal. — This  name  is  applied  to  those  varieties 
of  bituminous  coals  which  do  not  stick  or  melt  together  in  the 
fire.     For  this  reason  they  are  sometimes  called  "free  burning." 
Such  coals  are  valuable  for  use  under  boilers  because  of  the  clean 
fires  which  they  give.     The  structure  of  this  variety  of  coal  is  in 
layers,  which,  when  broken  at  right  angles  to  the  layers,  show  a 
bright  shiny  surface. 

115.  Cannel  Coal. — This' is  a  variety  of  bituminous  coal  which 
is  very  rich  in  carbon.     It  differs  in  appearance  from  other  coals 
in  being  very  compact  and  having  a  dull  luster.     When  broken, 
the  cleavage  does  not  seem  to  follow  any  particular  line.     It 
kindles  easily  and  burns  freely  with  a  bright  flame  resembling 
that  of  a  candle,  from  which  fact  its  name  is  derived.     It  varies 
in  fixed  carbon  from  about  40  to  55  per  cent  and  in  volatile 
matter  from  about  43  to  55  per  cent,  and  from  its  richness  in 
hydrocarbons  it  is  very  valuable  in  gas-making. 

116.  Semi -bituminous  Coals. — These  resemble  the  anthracite 
more  closely  than  the  bituminous,  but  they  are  lighter,  and 
kindle  and  burn  more  readily.     When  they  burn  they  give  off  an 
intense  heat  with  very  little  smoke,  and  being  free-burning  it  is 


142  STEAM  BOILERS 

easy  to  keep  a  clean,  good  fire  which  requires  but  little  attention. 
For  these  reasons,  semi-bituminous  coal  is  very  desirable  as  a 
steam-producing  coal.  In  analysis  it  runs  about  as  follows: 
fixed  carbon,  70  per  cent;  volatile  matter,  16  per  cent;  sulphur, 
0.75  per  cent;  ash,  12  per  cent. 

117.  Semi -anthracite. — Coal  which  contains  from  7  to  12  per 
cent  of  volatile  combustible  matter  is  classed  as  semi-anthracite. 
It  kindles  and  burns  more  readily  than  anthracite,  is  lighter,  not 
so    hard,   and  has  not  so  much  of  a  metallic   luster   as    true 
anthracite. 

A  sample  of  this  coal  analyzes  about  as  follows:  fixed  car- 
bon, 88.90  per  cent;  volatile  matter,  7.68  per  cent;  ash,  3.49  per 
cent. 

118.  Anthracite. — This  coal  ignites  and  burns  with  a  short 
yellowish-blue  flame  and  without  giving  off  smoke.     It  contains 
only  from  3  to  7  per  cent  of  volatile  combustible  matter,  which 
accounts  for  its  short  flame,  but  when  ignited,  gives  off  an  intense 
heat  due  to  the  combustion  of  the  almost  pure  carbon  of  which 
it  is   composed.     This   coal  is   distinguished  by  its  hardness, 
density,  and  high  specific  gravity  and  by  its  metallic  luster. 

The  standard  commercial  sizes  are: 

Egg  coal,  which  must  pass  a  2f-in.  mesh  but  not  through  a  2-in.  mesh. 

Stove  coal,  which  must  pass  a  2-in.  mesh  but  not  through  a  l£-in.  mesh. 

Chestnut  coal,  which  must  pass  a  1^-in.  mesh  but  not  through  a  3/4-in. 
mesh. 

Pea  coal,  which  must  pass  a  3/4-in.  mesh  but  not  through  a  1/2-in.  mesh. 

Buckwheat  No.  1,  which  must  pass  a  1/2-in.  mesh  but  not  through  a  1/4-in. 
mesh. 

Buckwheat  No.  2,  which  must  pass  a  1/4-in.  mesh  but  not  through  a  1  /8-in. 
mesh. 

An  average  analysis  of  this  coal  shows  it  to  contain  fixed  carbon 
89.5  per  cent;  volatile  matter,  4.5  per  cent;  ash,  6.0  per  cent. 
The  percentage  of  ash  is  lower  in  the  larger  sizes  of  coal  and 
higher  in  the  smaller  sizes,  increasing  by  about  1 J  per  cent  from 
one  size  to  the  next  smaller  size. 

119.  Petroleum. — The  only  natural  liquid  fuel  of  any  impor- 
tance is  crude  petroleum.     Petroleum  has  a  high  heating  value, 
ranging  from  18,000  to  20,000  B.t.u.  per  pound;  therefore,  it  is 
possible  to  have  a  great  amount  of  energy  stored  in  a  small  space. 
Kerosene,  benzine,  and  gasoline  are  all  made  by  distilling  petro- 


FUELS  143 

leum,  but,  while  these  substances  have  a  high  heating  value, 
they  are  not  suitable  as  boiler  fuels  on  account  of  their  cost. 

There  are  two  kinds  of  petroleum  found  in  the  United  States, 
that  which  yields  a  paraffin  residue  on  being  distilled,  and 
that  which  yields  asphalt.  The  former  is  found  in  the  East  and 
Middle  West  and  yields  such  a  variety  of  valuable  light  oils, 
that  the  crude  product  is  too  valuable  to  be  used  as  fuel.  Prac- 
tically all  of  this  oil  is  refined  to  obtain  the  more  valuable  and 
lighter  oils.  The  asphaltic  variety  is  found  in  Texas  and 
California  and  is  used  mostly  for  fuel. 

In  general,  petroleum  is  of  a  brownish  color  tinged  with 
green,  and  it  consists  mostly  of  carbon  and  hydrogen.  It  also 
contains  a  certain  percentage  of  water  varying  from  1  to  50 
per  cent,  but,  if  the  oil  is  handled  properly  when  taken  from  the 
well,  the  water  may  be  separated.  As  the  water  is  a  detriment, 
one  should  be  careful  in  buying  oil  to  see  that  the  percentage  of 
water  is  low.  The  amount  of  water  and  dirt  in  the  oil  may  be 
determined  by  mixing  a  small  quantity  of  it  with  an  equal 
quantity  of  gasoline  and  allowing  it  to  stand  in  a  warm  place 
for  24  hours,  when  the  dirt  and  water  will  settle  to  the  bottom. 

A  sample  of  Texas  oil  analyzed  as  follows:  carbon,  85.66  per 
cent;  hydrogen,  11.03  per  cent;  oxygen,  3.31  per  cent.  The 
heating  value  of  this  oil  is  19,240  B.t.u.  per  pound. 

120.  Heating  Value  of  Fuels.— The  fuel  elements  which  gener- 
ate heat  on  being  burned  are  carbon,  hydrogen,  and  sulphur, 
though  the  latter  is  rarely  ever  present  in  sufficient  quantities  to 
be  very  important  and  is  considered  undesirable  on  account  of 
the  acid  formed  when  it  burns. 

In  the  process  of  burning,  these  fuel  elements  unite  with 
oxygen,  and  in  doing  so  liberate  a  definite  amount  of  heat  for 
each  pound  of  the  fuel  element  which  is  so  united.  The  carbon 
may  form  one  of  two  substances.  If  there  is  sufficient  oxygen 
present  and  the  carbon  is  brought  into  contact  with  it,  carbon 
dioxide  will  be  formed.  This  is  the  product  resulting  from 
complete  combustion  of  the  carbon,  since  it  has  united  with  all 
the  oxygen  possible.  If  there  is  not  sufficient  oxygen  present, 
the  compound  formed  will  be  carbon  monoxide. 

The  hydrogen  unites  with  oxygen  and  forms  water,  and  the 
sulphur  unites  with  oxygen  to  form  sulphurous  acid,  SO2. 
These  chemical  combinations  of  the  substances  liberate  heat 
to  the  extent  shown  by  the  following  table: 


144  STEAM  BOILERS 

1  lb.  of  carbon  burned  to  CO2  ..........  14,500  B.t.u. 

1  lb.  of  carbon  burned  to  CO  ...........  4400  B.t.u. 

1  lb.  of  hydrogen  burned  to  H2O  ........  62,100  B.t.u. 

1  lb.  of  sulphur  burned  to  SO2  ..........  4000  B.t.u. 

1  lb.  of  CO  burned  to  CO2  .............  4330  B.t.u. 

Whatever  oxygen  the  fuel  may  contain  is  considered  to  be 
already  combined  with  a  part  of  the  hydrogen  in  the  form  of  water 
and,  therefore,  the  amount  of  hydrogen  available  for  combination 
with  the  oxygen  of  the  air  in  the  process  of  burning  and  hence  for 
the  production  of  heat,  will  be  the  total  amount  of  hydrogen  less 
that  which  is  in  combination  with  the  oxygen  in  the  coal.  As  8 
lb.  of  oxygen  will  combine  with  1  lb.  of  hydrogen,  the  part  of 
the  hydrogen  already  combined  with  the  oxygen  in  the  coal  will 

be  =•  where  0  represents  the  weight  of  oxygen,  and  this  quantity 

o 

must  be  subtracted  from  the  total  weight  of  hydrogen  in  the  coal. 


Thus  the  hydrogen  left  for  heat  production  will  be    H—^ 

and,  if  the  letters  H  and  0  represent  the  parts  of  a  pound  of  the 
hydrogen  and  oxygen,  then  the  heating  value  of  the  hydrogen 

will  be  62,100  (#-  Q)  •     If  the  part  of  a  pound  of  fuel  which  is 
V         o/ 

carbon  is  represented  by  C,  the  heat  obtained  from  the  combus- 
tion of  the  carbon  will  be  14,500  C,  and,  in  a  like  manner,  the 
heat  evolved  by  the  burning  of  the  sulphur  will  be  4000  S. 
Therefore,  the  entire  heating  value  of  the  fuel  will  be 


Heating  value  in  B.t.u.  =  14,  500C  +  62,100  H-  ^]  +40005. 

\          o  / 

If  C,  H,  0,  and  S  represent  the  weight  of  each  of  these  sub- 
stances in  a  pound  of  fuel,  the  heating  value  will  be  expressed 
in  B.t.u.  per  pound.  As  an  illustration  of  the  application  of  this 
formula,  we  will  find  the  heating  value  per  pound  of  coal  which 
analyzes  as  follows:  carbon,  80  per  cent;  hydrogen,  5  per  cent; 
oxygen,  2.7  per  cent;  nitrogen  1.1  per  cent;  sulphur,  1.2  per  cent; 
ash,  8.3  per  cent. 


B.t.u.  per  lb.  =14,5000  +  62,100   #-)  +4000S 

\          o  / 

-  14,  500  X.  80  +62,  100  (.05  ~'^}  +  4000X.012 


=  11,600+2894+48 
=  14,542 


FUELS 


145 


From  the  above  it  is  seen  that  of  the  entire  14,542  B.t.u.  in  the 
pound  of  coal,  the  carbon  furnishes  11,600,  the  hydrogen  2894, 
and  the  sulphur  only  48.  The  small  amount  furnished  by  the 
sulphur  might  well  be  neglected  and  this  is,  in  fact,  often  done. 
Owing  to  the  many  difficulties  in  the  way  of  getting  an  accurate 
analysis  of  coal  and  to  the  length  of  time  taken,  it  is  better  and 
quicker  to  find  the  heating  value  of  coal  by  means  of  a  coal 
calorimeter,  which  is  an  instrument  in  which  the  coal  is  actually 
burned  and  the  heat  which  is  evolved  is  measured.  A  detailed 


16000 


15500 


15000 


14  500 


14  000 


&  13  500 
p 

H 

ri 

13000 


12500 


12000 


\ 


40  50  60  70  80  90  100 

Per  Cent  of  Fixed  Carbon  per  Pound  of  Combustible, 
Dry  and  Free  from  Ash 
FlG.   72. 

account  of  this  apparatus  and  its  operation  may  be  found  in 
books  on  Fuels. 

Owing  to  the  time  required  and  the  difficulty  in  making  an 
ultimate  analysis,  it  is  not  usually  done  in  commercial  work, 
but  instead,  the  proximate  analysis  is  made  as  this  can  be  done 
in  a  much  shorter  time.  For  this  reason  we  see  the  proximate 
analysis  of  a  coal  stated  much  oftener  than  the  ultimate.  It 
would  be  very  desirable  to  have  some  short  method  of  calculating 


146  STEAM  BOILERS 

the  heating  value  of  a  fuel  from  its  proximate  analysis,  as  may 
be  done  from  the  ultimate  analysis.  Several  equations  for 
doing  this  have  been  proposed  but  none  of  them  seem  to  give 
very  satisfactory  results  when  applied  to  American  coals. 

To  accomplish  the  same  results,  the  heating  values  of  a  great 
many  American  coals  have  been  plotted  on  the  curve  shown  in 
Fig.  72.  If  the  proximate  analysis  of  a  coal  is  known,  its  heating 
value  can  be  obtained  from  this  curve  with  a  fair  degree  of 
accuracy. 

As  the  exact  composition,  and  hence  the  heating  value  of  that 
part  of  the  coal  known  as  the  volatile  matter,  is  quite  variable, 
it  is  reasonable  to  suppose  that  where  the  analysis  shows  a  small 
percentage  of  fixed  carbon  in  the  combustible  matter,  or  in  other 
words,  a  large  portion  of  volatile  matter,  the  curve  will  not  be 
as  accurate  as  when  the  fixed  carbon  is  large.  In  general,  the 
curve  will  give  results  which  are  within  5  per  cent  of  the  true 
heating  value  of  the  coal,  and  this  is  close  enough  for  many 
purposes. 

To  illustrate  the  use  of  the  curve,  consider  a  sample  of  Illinois 
coal  showing  the  following  proximate  analysis. 

Moisture 5 . 96  per  cent 

Volatile  matter 30 . 29  per  cent 

Fixed  carbon .  > 52 . 16  per  cent 

Ash 1 1 . 59  per  cent 


100.00  per  cent 

The  ash  and  moisture  are  not  combustible.     Therefore,  the 
combustible  consists  of 

Volatile  matter 30 . 29  per  cent 

Fixed  carbon 52 . 16  per  cent 


82.45  per  cent 
and  the  per  cent  of  fixed  carbon  per  pound  of  combustible  is 

52.164-82.45-63.3  percent. 

Finding  the  percentage  63.3  on  the  base  line  of  the  curve  and 
following  this  point  upward  until  we  reach  the  curve,  then  looking 
opposite  this  point  to  the  left-hand  margin,  we  find  the  heating 
value  per  pound  of  combustible  to  be  15,225  B.t.u.  As  the 
combustible  forms  only  82.45  per  cent  of  the  coal,  the  heating 
value  per  pound  of  coal  is 

15,225 X. 8245 -12,553  B.t.u. 


CHAPTER  X 
CHEMISTRY  OF  COMBUSTION 

121.  Combustion. — Combustion  may  be  defined  as  the  chemical 
union  of  a  substance  with  oxygen,  accompanied  by  the  giving 
oft"  of  light  and  heat.     Some  substances  unite  with  oxygen  so 
slowly  as  not  to  give  off  light,  and  this  process  would  not  be 
called  combustion.     Such  is  the  case  when  iron  rusts.     The  same 
amount  of  heat  is  given  off,  however,  whether  the  process  takes 
place  slowly  or  rapidly.     The  substance  that  burns  is  called  the 
combustible  while  the  oxygen  is  the  supporter  of  combustion. 

122.  Oxygen. — Oxygen  is  the  universal  supporter  of  combus- 
tion and  our  largest  source  of  supply  for  it  is  the  atmosphere. 
Although  oxygen  is  one  of  the  most  common  substances,  yet  it 
is  never  found  alone  in  nature,  but  is  always  associated  with  some 
other  substance,  being  either  combined  with  it,  or  merely  in  the 
form  of  a  mechanical  mixture.     By  a  combination  of  substances 
is  meant  the  union  of  them  into  a  single  substance,  as  when 
hydrogen  and  oxygen  unite  to  form  water.     In  a  mechanical 
mixture  the  substances  are  not  united  but  are  simply  mixed  and 
each  retains  all  its  original  characteristics.     Air  is  a  mechanical 
mixture  of  oxygen  and  nitrogen  in  the  following  proportions. 

COMPOSITION  OF  AIR 

Parts  by  volume  Parts  by  weight 

Oxygen .207  .23 

Nitrogen .  793  . 77 

Nitrogen  is  an  inert  substance,  that  is,  it  does  not  combine 
readily  with  other  substances  and  seems  to  be  there  merely  for 
the  purpose  of  diluting  the  oxygen.  The  above  proportions  of 
oxygen  and  nitrogen  seem  to  be  fairly  constant  in  air  taken  from 
any  part  of  the  earth.  Besides  these  substances,  there  are  small 
amounts  of  other  gases  in  air,  but  they  are  present  in  such  small 
quantities  that  we  need  not  consider  them  here. 

Oxygen  is  a  very  active  substance  and  under  favorable  condi- 
tions combines  readily  with  almost  any  other  element. 

147 


148  STEAM  BOILERS 

123.  Carbon. — Of  all  combustible  substances  found  in  nature, 
the  most  common  and  easily  obtained  is  carbon  and  it  is  by 
reason  of  the  large  amounts  contained;  in  coal,  wood,  and  other 
fuels,  that  these  substances  are  so  valuable  as  fuels. 

Carbon  is  an  infusible,  non-volatile  substance  which  is  found 
in  nature  in  three  forms:  viz.,  (1)  diamond,  (2)  plumbago  or 
graphite,  (3)  charcoal  or  lampblack.  Among  natural  fuels, 
anthracite  coal  approaches  most  nearly  to  pure  carbon  and  is 
classed  between  graphite  and  charcoal,  while  of  the  artificial 
fuels,  coke  has  a  very  large  percentage  of  carbon. 

124.  Chemical  Definitions. — All  substances  are  either  elements, 
compounds,  or  mixtures. 

An  Element  is  a  substance  which,  so  far  as  we  know  at  present, 
cannot  be  broken  up  into  any  simpler  form.  Iron,  carbon, 
silver,  hydrogen,  oxygen,  and  nitrogen  are  all  elements  and  there 
are  a  great  many  more  that  need  not  be  considered  here. 

A  Compound  is  a  substance  which  can  be  broken  up  into 
simpler  forms  by  chemical  process  and  is  thus  known  to  be  a 
combination  of  certain  elements.  Water  is  a  compound  and  we 
find  by  decomposing  it  that  hydrogen  and  oxygen  are  the  ele- 
ments which  compose  it.  Carbonic  acid  is  a  compound  formed 
by  the  union  of  carbon  and  oxygen. 

A  compound  is  represented  by  a  formula  composed  of  the 
letters  representing  the  elements  of  which  the  compound  is  com- 
posed. For  example,  H20  is  the  formula  for  water,  and  indicates 
that  two  atoms  of  hydrogen  are  combined  with  each  atom  of 
oxygen  in  forming  the  water.  C02  is  the  formula  which  rep- 
resents carbonic  acid,  and  indicates  that  two  atoms  of  oxygen 
have  combined  with  one  of  carbon. 

A  Mixture  consists  of  two  or  more  substances  that  are  merely 
mingled  together  without  causing  any  chemical  change  in  any 
of  the  ingredients.  Coal  is  a  mixture  of  moisture,  ash,  fixed 
carbon,  and  volatile  matter.  The  air  is  a  mixture  of  nitrogen 
and  oxygen. 

125.  Molecules  and  Atoms. — If  a  substance  were  divided  and 
redivided  into  particles,  until  we  had  the  smallest  particle  of  that 
substance  which  could  exist  by  itself  without  losing  the  nature 
of  the  substance,  we  would  have  what  is  known  as  a  Molecule  of 
that  substance,  and,  if  this  molecule  were  broken  up  into  the 
chemical  elements  which  make  it  up,  these  new  divisions  would 
be  what  are  called  Atoms  and  are,  presumably,  indivisible.     The 


CHEMISTRY  OF  COMBUSTION 


149 


chemical  symbols  for  compounds  indicate  to  us  the  numbers  and 
kinds  of  atoms  which  are  contained  in  each  molecule  of  the 
compound.  For  example,  the  symbol  H2Q  for  water  indicates 
that  two  atoms  of  hydrogen  and  one  atom  of  oxygen  comprise 
one  molecule  of  water.  The  symbol  for  ethyl,  or  grain,  alcohol 
is  C2H6O  and  from  this  symbol  we  know  that  one  molecule  of 
alcohol  contains  two  atoms  of  carbon,  six  of  hydrogen,  and  one  of 
oxygen.  As  a  rule  atoms  seldom  exist  uncombined,  as  they 
have  a  tendency  to  combine  with  other  atoms  unless  conditions 
are  such  as  to  prevent  it.  This  tendency  of  atoms  to  com- 
bine, explains  why  a  molecule  of  hydrogen  gas  has  two 
atoms  of  hydrogen.  Similarly,  the  molecules  of  oxygen  and 
nitrogen  also  each  contain  two  atoms.  In  other  words,  if  an 
atom  of  a  substance  has  nothing  else  to  combine  with,  it  will 
unite  with  one  or  more  atoms  like  itself. 

126.  Atomic  Weights. — The  atoms  of  different  substances  have 
different  weights  and,  as  that  of  hydrogen  is  the  lightest,  its 
atomic  weight  is  generally  given  as  1  and  the  weights  of  the 
other  atoms  are  given  in  terms  of  that  of  hydrogen. 

The  following  table  gives  the  atomic  weights  of  the  elements 
which  need  to  be  dealt  with  in  the  study  of  fuels. 


Element 

Symbol 

Atomic  weight 

Hvdroffen 

H 

1 

Carbon  

C 

12 

Sulphur 

s 

32 

Oxygen  

0 

16 

Nitrogen  

N 

14 

127.  Molecular  Weights. — When  two  or  more  elements  com- 
bine to  form  a  compound,  the  relative  weight  of  the  molecule 
of  the  compound  will  equal  the  sum  of  the  weights  of  the  atoms 
which  comprise  it.  This  is  called  the  molecular  weight  of  the 
compound.  One  atom  of  oxygen  combines  with  two  of  hydro- 
gen to  form  water,  and  from  this  we  see  that  the  molecular  weight 
of  water  equals  the  weight  of  one  atom  of  oxygen  (  =  16)  plus  the 
weight  of  the  two  atoms  of  hydrogen  (  =  2),  so  that  the  molecular 
weight  of  water  is  18.  From  this  we  gather  that  2/ 18  of  the  water 
by  weight  is  hydrogen  and  16/18  is  oxygen.  The  molecular 


150  STEAM  BOILERS 

weight  of  CO2  =  12  +32  =  44.  By  weight,  12/44  is  carbon  and 
32/44  is  oxygen.  Twelve  pounds  of  carbon  and  32  Ib.  of 
oxygen  will  form  44  Ib.  of  CO2. 

128.  Compounds  of  Carbon  and  Oxygen.  —  Some  substances 
will  unite  with  oxygen  in  more  than  one  proportion.  Such  is 
the  case  with  carbon.  If  there  is  an  abundant  supply  of  oxygen 
present  and  the  conditions  are  favorable,  each  atom  of  carbon 
will  take  up  two  atoms  of  oxygen.  This  is  the  greatest  number 
of  atoms  of  oxygen  which  one  atom  of  carbon  ever  takes  up.  If 
the  atom  of  carbon  unites  with  two  atoms  of  oxygen  complete 
combustion  takes  place,  since  there  is  an  abundant  supply 
of  oxygen.  The  product  of  this  union  of  the  carbon  and  oxy- 
gen is  CO  2,  which  is  variously  called  carbonic  acid,  carbon 
dioxide,  or  most  often  by  merely  the  chemical  formula  CO2. 
When  the  carbon  is  burned  completely  to  CO2  there  will  be  given 
off  14,500  B.t.u.  for  every  pound  of  carbon  burned.  This 
quantity  is  called  the  heat  of  complete  combustion  of  carbon. 

If,  on  the  other  hand,  there  is  not  a  sufficient  supply  of  oxygen 
present,  then  each  atom  of  carbon  will  unite  with  only  one- 
atom  of  oxygen  and  the  product  will  be  carbon  monoxide,  whose 
chemical  symbol  is  CO.  When  carbon  unites  with  oxygen  to 
form  carbon  monoxide  there  are  only  4400  B.t.u.  given  off  for 
every  pound  of  carbon  burned.  This  shows  the  importance  of 
securing  complete  combustion  in  the  furnace  since,  for  every 
pound  of  carbon  burned,  there  is  a  loss  of  14,500-4400  =  10,100 
B.  t.u.  if  the  combustion  is  incomplete. 

Carbon  dioxide  is  a  colorless  gas  one  and  a  half  times  heavier 
than  air,  and  has  a  slightly  acid  taste  and  smell.  It  is  incom- 
bustible since  it  is  already  the  product  of  complete  combustion. 
It  is  not  a  direct  poison  but  it  will  not  support  animal  life  or 
combustion. 

Carbon  monoxide  gas  is  slightly  lighter  than  air,  is  colorless 
and  ordorless.  It  is  a  direct  poison  and  is  dangerous  because 
when  it  enters  the  system  it  takes  up  oxygen  from  the  blood. 
Since  it  is  the  product  of  incomplete  combustion  it  will  burn,  and 
in  so  doing  take  up  one  more  atom  of  oxygen  for  every  molecule 
of  carbon  monoxide,  thus  forming  CO2.  The  process  may  be 
represented  by 


When  CO  burns  to  CO2  there  will  be  given  off  10,100  B.t.u,  for 


CHEMISTRY  OF  COMBUSTION  151 

every  pound  of  carbon  involved  in  the  operation,  but  for  every 
pound  of  carbon  monoxide  burned  there  will  be  given  off  only  4330 
B.t.u.,  since  1  Ib.  of  carbon  monoxide  contains  only  a  fraction 
of  a  pound  of  carbon. 

129.  Process  of  Combustion  of  Fuel. — Besides  carbon,  coal 
contains  other  substances  in  smaller  quantities,  such  as  hydrogen, 
oxygen,  sulphur,  and  also  the  incombustible  matter  which  is 
called  ash.  The  hydrogen  is  combined  with  a  part  of  the  carbon 
in  a  series  of  compounds  called  hydrocarbons.  This  series  of 
hydrocarbons  consists  of  about  50  compounds,  the  simplest  of 
which  is  CH4  and  ranging  from  this  to  the  most  complex  forms 
of  carbon  and  hydrogen.  These  hydrocarbons  are  very  inflam- 
mable and  when  burned  they  are  split  up  into  simpler  and 
simpler  forms  until  finally  all  the  carbon  is  united  with  oxygen 
to  form  CO2  if  the  combustion  is  complete,  and  the  hydrogen 
unites  with  oxygen  to  form  water,  H2O. 

As  there  is  a  large  percentage  of  carbon  in  coal,  there  is  much 
more  than  is  needed  to  make  up  the  hydrocarbon  compounds. 
All  the  carbon  which  is  not  thus  combined  is  known  as  the  fixed 
carbon. 

It  may  thus  be  seen  that  the  process  of  combustion  is  a  very 
complicated  one  and  it  is  impossible  to  tell  exactly  what  does 
take  place  in  the  furnace  of  a  boiler.  Associations  and  dissocia- 
tions of  the  elements  in  the  fuel  occur  in  rapid  succession.  Com- 
binations which  are  formed  at  first  are  later  split  up  by  the  intense 
heat  and  their  parts  again  unite  into  the  same  or  simpler  com- 
binations. But,  whatever  the  process,  it  is  certain  that  the 
products  of  complete  combustion  should  be  carbon  dioxide  (CO2), 
water  (H2O),  nitrogen  (N2),  and  perhaps  a  small  quantity  of 
sulphurous  acid  (S02),  while  if  the  combustion  is  incomplete 
there  will  be  some  carbon  monoxide  (CO)  and  less  CO2. 

While  we  do  not  know  exactly  the  order  of  events  in  the  com- 
bustion of  coal  we  may  say  in  a  general  way  that  when  the  fresh 
coal,  say  of  a  bituminous  character,  is  thrown  on  the  fire,  it 
absorbs  some  heat  from  the  fire  in  being  warmed  and  the  fire  is 
cooled  thereby.  When  the  coal  is  heated  to  212°,  the  moisture 
contained  in  it  begins  to  evaporate  and  this  cools  the  fire  more, 
since  heat  is  abstracted  from  the  fire  in  order  to  evaporate  the 
moisture.  At  a  temperature  of  about  220°  the  volatile  hydro- 
carbons begin  to  be  driven  off  and,  mixing  with  air  and  passing 
over  the  hot  bed  of  coal,  burn  into  C02  and  water.  During  this 


152  STEAM  BOILERS 

stage  of  the  combustion  it  is  very  important  that  the  hydro- 
carbons be  mixed  with  a  sufficient  supply  of  air  to  insure  their 
being  burned  completely,  and  for  this  purpose  considerable  air 
should  be  admitted  through  the  fire  doors  above  the  fire  so  as  to 
come  into  direct  contact  with  the  hydrocarbons.  If  the  particles 
of  carbon  liberated  by  the  splitting  up  of  the  hydrocarbon 
compounds  do  not  immediately  meet  with  sufficient  oxygen,  they 
will  unite  with  only  one  atom  of  oxygen,  forming  CO,  and,  by 
the  time  they  have  come  in  contact  with  sufficient  oxygen,  they 
may  be  cooled  to  so  low  a  temperature  that  the  union  is  impos- 
sible, and  the  carbon  will  then  pass  out  as  the  product  of  incom- 
plete combustion,  CO.  Thus  it  is  seen  to  be  of  extreme  im- 
portance to  insure  that  the  carbon  be  burned  completely  to  C02 
before  it  is  allowed  to  be  cooled  by  coming  in  contact  with  any 
metal  surfaces,  such  as  the  tubes  or  the  shell  of  a  boiler. 

During  the  combustion  of  the  fixed  carbon  left  on  the  grate 
the  following  process  is  assumed  to  take  place.  The  air  passes 
through  the  grate  and,  encountering  incandescent  carbon,  the 
plentiful  supply  of  oxygen  causes  the  formation  of  C02.  Some 
of  this  gas  will  take  up  more  carbon  and  form  CO  as  it  passes 
upward  through  the  fuel  bed.  If  there  is  sufficient  oxygen  left 
uncombined,  this  CO  will  immediately  burn  to  CO2.  There  is 
always,  however,  some  CO  in  the  gases  rising  from  the  top  of  the 
fuel  bed  and  the  uniting  of  this  CO  with  the  oxygen  necessary  to 
form  CO2  explains  the  short  blue  flames  usually  seen  at  the  top 
of  a  coke  fire.  Unless  this  CO  is  brought  in  contact  with  an 
excess  of  oxygen  above  the  fire  it  will  pass  out  of  the  chimney 
in  the  form  of  CO,  with  its  attendant  loss  of  heat  as  pointed  out 
before.  This  points  again  to  the  necessity  for  securing  complete 
combustion  of  the  carbon  before  it  leaves  the  furnace,  .for  once 
it  has  left  the  furnace  in  the  form  of  CO  there  is  small  chance  of 
its  combining  with  more  oxygen  to  form  C02,  as  this  operation 
requires  a  high  temperature  and  the  further  away  from  the 
furnace  the  gas  gets  the  cooler  it  becomes. 

130.  Air  Required  for  Combustion. — From  a  knowledge  of  the 
atomic  weights  of  substances  and  the  composition  of  air  we  may 
readily  calculate  the  air  required  for  combustion  of  any  fuel, 
if  we  know  the  composition  of  the  fuel.  The  process  is  best 
illustrated  by  an  example.  Suppose  we  wish  to  calculate  the 
amount  of  air  required  to  burn  a  certain  kind  of  Illinois  coal 
having  the  following  composition. 


CHEMISTRY  OF  COMBUSTION  153 

Parts  to  1  Ib. 


Hydrogen  
Oxvsren 

5  .  26  per  cent.  .  . 
8  35  per  cent. 

.  .  .   0.0526 
.  .   0  .  0835 

Nitrogen 

1  33  per  cent 

0  0133 

Sulphur  
Ash 

2  .  02  per  cent.  .  . 
13  24  per  cent. 

...   0.0202 
.   0  1324 

100.00  1.0000 

The  nitrogen  and  the  ash  take  no  part  in  the  combustion,  so 
we  have  to  consider  only  the  carbon,  hydrogen,  oxygen,  and 
sulphur. 

We  have  already  seen  that  in  forming  water,  1  Ib.  of  hydrogen 
will  unite  with  8  Ib.  of  oxygen.  This  is  obtained  from  the 
atomic  weights. 

H2:O  =  (2X1):(1X16)=2:16  =  1:8 

If  the  carbon  is  burned  completely  the  product  will  be  CO2 
and,  since  the  atomic  weight  of  carbon  is  12,  the  proportion  of 
oxygen  to  carbon  will  be  -*j 

O2:C  =  (2 X 16)  :12  =32:12=2§:1 

In  other  words,  2§  Ib.  of  oxygen  are  required  to  burn  1  Ib. 
of  carbon  to  CO2. 

In  the  same  way,  the  atomic  weight  of  sulphur  is  32,  and  in 
burning  to  sulphurous  acid  SO2,  the  oxygen  required  may  be 
found  from  the  proportion  of  oxygen  to  sulphur. 

O2:S  =  (2X16):32=32:32  =  1:1    Or   1  Ib.  of  oxygen  is  re- 
quired to  burn  1  Ib.  of  sulphur  to  S02. 

We  may  consider  that  all  the  oxygen  that  is  in  the  coal  is 
already  combined  with  a  part  of  the  hydrogen,  rendering  it 
inert  as  far  as  combustion  is  concerned.  Thus  the  .0835  of  a 

QQO  C 

pound  of  oxygen  will  be  already  combined  with  — = —  =  .01041b.  of 

hydrogen.     Enough  oxygen  will  have  to  be  supplied  in  the  air 
then  to  combine  with 

Carbon  =    .  6980  Ib. 

Hydrogen  .0526 -.0104     =    .0422  Ib. 

Sulphur  =    .02021b. 

The  carbon  will  require        .  698   X  2f  =  1 . 861     Ib.  of  oxygen. 

The  hydrogen  will  require    .0422X8    =    .3376  Ib.  of  oxygen. 

The  sulphur  will  require       .0202X  1    =    .0202  Ib.  of  oxygen. 


Making  the  total  oxygen  required  2.2188  Ib. 


154  STEAM  BOILERS 

As  air  contains  .23  parts  by  weight  of  oxygen,  the  weight  of  air 
which  will  contain  2.2188  Ib.  of  oxygen  will  be  2.2188  -^. 23  =9.64 
and  this  is  the  amount  of  air  needed  to  supply  sufficient  oxygen 
to  completely  burn  1  Ib.  of  the  fuel  mentioned  above.  As  1 
Ib.  of  air  at  62°F.,  has  a  volume  of  13.14  cu.  ft.,  9.64  Ib.  would 
occupy  a  volume  of  9.64  X 13. 14  =  126.67  cu.  ft.  and  this  quantity 
of  air  would  have  to  be  admitted  to  the  furnace  for  every  pound 
of  coal  burned. 

For  approximate  determination  of  the  air  required  for  com- 
bustion the  following  formula  may  be  used. 

Weight  of  air  -  12C  +35 

in  which  C,  H,  and  0  represent  the  parts  of  a  pound  of  carbon, 
hydrogen,  and  oxygen  respectively  in  a  pound  of  the  coal. 
By  this  formula,  the  sample  of  coal  we  have  just  been  consider- 
ing would  require 


12 X .698  +35 (.0526  - 


=  8.38+35 X .0422  =  8.38  + 1.47 - 9.85  Ib. 

which  is  quite  close  to  the  result  obtained  before.  As  it  is 
unnecessary  for  practical  purposes  to  calculate  accurately  the 
amount  of  air  required  to  burn  coal,  and  as  most  fuels  require 
between  11  and  12  Ib.  of  air  per  pound  of  fuel,  it  is  usual  to  con- 
sider that  12  Ib.  of  air  will  be  required  to  burn  each  pound  of  coal. 
When  it  is  considered  how  complicated  the  chemical  actions 
are  and  how  great  the  chances  that  the  carbon  will  not  meet  its 
full  complement  of  oxygen,  it  will  readily  be  seen  that  it  is 
necessary  to  admit  more  air  into  the  furnace  than  is  actually 
required  to  burn  the  coal,  in  order  to  be  sure  that  each  atom  of 
carbon  will  meet  an  abundance  of  oxygen.  This  excess  air  is 
sometimes  called  air  of  dilution  because  it  dilutes  the  gases  rising 
from  the  fire  and  mingles  with  them,  giving  each  atom  of  caabon 
an  opportunity  to  combine  with  as  much  oxygen  as  it  will. 
The  amount  of  excess  air  necessary  depends  upon  the  draft  of 
the  chimney;  the  weaker  the  draft,  the  more  air  of  dilution  is 
required.  It  is  usual  to  supply  twice  as  much  air  as  is  actually 
required  for  combustion  when  natural  draft  is  used  and  one  and 
one-half  times  as  much  when  forced  draft  is  used.  The  air  of 
dilution  is  then  100  per  cent  for  chimney  draft  and  50  per  cent 
for  forced  draft. 


CHEMISTRY  OF  COMBUSTION 


155 


131.  Flue  Gas. — A  sample  of  the  products  of  combustion 
leaving  a  furnace  may  be  collected  and  analyzed  by  a  simple 
method,  and  this  gives  a  check  on  the  way  in  which  the  fires  are 
being  handled.  It  has  been  shown  that -an  excess  of  air  must  be 
admitted  to  the  furnace  in  order  to.  complete  the  combustion. 
If  the  air  supply  is  not  sufficient,  some  of  the  carbon  cannot 


FIG.  73. — Orsat  flue  gas  apparatus. 

burn  completely,  and  this  will  be  indicated  by  CO  showing  in 
the  flue  gases,  as  the  products  of  combustion  are  called. 

The  amount  of  oxygen  present  in  the  flue  gases  gives  an 
indication  of  the  amount  of  excess  air  admitted  to  the  furnace, 
and  the  amounts  of  CO  and  CO2  indicate  the  completeness  of 
the  combustion.  From  what  has  been  said  before,  it  will  be 
seen  that  the  flue  gases  will  consist  of  CO2  and  CO,  formed  by 
the  burning  of  the  carbon;  steam  or  water  vapor  formed  by  the 
burning  of  hydrogen;  oxygen  which  is  supplied  in  greater  quan- 


156  STEAM  BOILERS 

titles  than  actually  needed  to  carry  on  combustion  and  some  of 
which  therefore  must  pass  out  of  the  chimney  in  the  form  of 
oxygen;  and  nitrogen,  which  is  inert  and  plays  no  part  in  the 
combustion. 

The  amount  of  these  constituents  present  in  the  flue  gas, 
except  the  steam,  which  condenses  at  the  temperatures  at  which 
the  analysis  must  be  made  and  which  therefore  disappears  from 
the  gas,  may  be  found  by  means  of  a  simple  device  called  an 
Orsat  Apparatus  (see  Fig.  73).  This  consists  of  three  pipeftes, 
D,  E,  and  F,  filled  respectively  with  caustic  potash,  a  mixture 
of  caustic  potash  and  pyrogallic  acid  or  pyrogallol,  and  cuprous 
chloride.  A  measuring  burette,  A,  is  also  attached  to  the  ap- 
paratus. A  sample  of  the  flue  gas,  say  100  c.c.  (cubic  centi- 
meters), is  taken  into  the  measuring  burette  and  then  passed  to 
the  pipette  D  containing  the  caustic  potash,  which  absorbs  all 
the  CO2.  If  the  volume  of  the  gas  is  noted  before  and  after  the 
absorption,  the  difference  will  be  the  amount  of  CO2  present  in 
the  flue  gas.  The  gas  is  then  passed  through  the  second  pipette 
E  containing  the  mixture  of  caustic  potash  and  pyrogallic  acid, 
which  absorbs  the  oxygen.  The  shrinkage  in  volume  will  be 
the  amount  of  oxygen  present  in  the  flue  gas.  In  the  same 
way,  the  CO  may  be  found  by  passing  the  remaining  gas  through 
the  third  pipette  .F  containing  the  cuprous  chloride,  which  ab- 
sorbs CO.  The  remaining  gas  may  be  considered  to  be 
nitrogen. 

If  the  combustion  had  been  complete  and  there  had  been  only 
enough  air  present  to  burn  the  fuel,  then  the  flue  gas  would  show 
by  analysis  only  CO2  and  N,  since  all  the  oxygen  would  be  com- 
bined with  the  carbon.  Since  air  consists  by  volume  of  oxygen 
.207  parts  and  nitrogen  .793  parts,  the  flue  gas  would  then  show 
by  analysis  CO2,  20.7  per  cent,  and  nitrogen  79.3  per  cent, 
because  CO2  occupies  the  same  volume  as  the  oxygen  from  which 
it  is  formed.  Now,  as  it  is  necessary  to  supply  about  100  per 
cent  excess  air,  the  percentage  of  CO2  will  be  much  less  than  20.7. 
Combustion  will  be  complete  when  the  percentage  of  CO2  lies 
between  10  and  12  and  when  there  is  no  CO,  and  the  furnace 
should  be  so  handled  that  these  results  will  be  obtained. 

No  more  excess  air  should  be  admitted  to  the  furnace  than  is 
required  to  secure  complete  combustion,  as  the  air  chills  the 
fire  and  also  causes  a  loss  of  heat  by  carrying  off  heat  up  the 
chimney.  The  heat  lost  in  this  way  will  depend  on  the  weight  of 


CHEMISTRY  OF  COMBUSTION  157 

gases  passing  up  the  chimney,  being  equal  to  the  weight  of  flue 
gases  times  their  average  specific  heat  times  the  difference  in  tem- 
perature through  which  they  have  to  be  heated.  The  average 
specific  heat  of  the  flue  gases  is  about  .25  and  their  temperature 
will  usually  be  between  400°  and  500°.  If  we  consider  the  room 
temperature  as  60°  the  difference  in  temperature  will  be  about 
(450-60)  =390°.  Now,  if  24  Ib.  of  air  are  admitted  for  every 
pound  of  coal  burned  and  if  nine-tenths  of  the  coal  is  combustible 
and,  therefore,  passes  up  the  chimney  in  the  products  of  combus-( 
tion,  the  total  weight  of  the  flue  gas  will  be  about  24.9  Ib.  per 
pound  of  coal  burned.  The  loss  per  pound  of  coal  from  hot  gases 
passing  up  the  chimney  would  then  be 

24.9 X. 25X390  =  2428  B.t.u. 

Now  if  the  heating  value  of  the  coal  was  13,000  B.t.u.  per 

2428 

pound,  this  would  represent  a  loss  of  =18.7  per  cent  of 

loUUU 

the  total  heating  value  of  the  coal.  It  will  be  readily  seen  that 
the  greater  the  amount  of  air  used  the  greater  will  be  this  loss 
of  heat. 

132.  Flue -gas  Analysis. — The  sample  of  flue  gas  is  usually 
taken  from  the  breeching  between  the  boiler  proper  and  the 
stack,  and  preferably  at  a  point  where  the  flue  gases  are  just 
leaving  the  boiler.  A  sampler  may  be  constructed  in  the 
manner  indicated  in  Fig.  74.  The  sampling  tube  may  be  made 
from  a  piece  of  1/4-in.  gas  pipe  having  a  length  about  6  in. 
greater  than  the  width  of  the  breeching  at  the  point  where  the 
sample  is  to  be  taken.  A  washer  made  of  heavy  rubber  packing 
is  placed  on  the  sampling  tube  and  held  in  place  by  a  thin  steel 
washer  and  collar  on  each  side.  The  rubber  washer  should  have 
a  diameter  about  6  in.  greater  than  the  hole  in  the  breeching,  so 
it  may  be  held  closely  against  the  breeching  while  the  sample  of 
flue  gas  is  being  taken,  thus  excluding  air  from  the  sample. 
A  number  of  1/8-in.  holes  should  be  bored  in  the  sampling(tube 
in  order  that  the  sample  collected  may  come  from  different  por- 
tions of  the  breeching.  The  flexible  rubber  washer  allows  the 
sampling  tube  to  be  moved  around  over  the  cross-section  of  the 
flue,  thus  insuring  that  the  sample  collected  will  represent  the 
average  of  the  flue  gas  passing  out  of  the  stack. 

The  gas  can  be  conveniently  collected  by  means  of  the  appara- 
tus shown,  consisting  of  two  small  tanks,  each  of  about  a  gallon 
capacity.  Each  tank  has  a  valve  at  P  and  also  at  Q  as  indicated. 


158 


STEAM  BOILERS 


Connect  the  valves  Q  by  means  of  a  small  rubber  hose,  2  to  3  ft. 
in  length.  Connect  a  sampling  tube  to  one  of  the  valves  P  by 
means  of  a  rubber  hose  N.  In  preparation  for  collecting  a 
sample,  fill  the  tank  R  with  water  and  have  a  small  amount  of 
water  in  the  tank  AS,  just  barely  sufficient  to  cover  the  entrance 
to  the  valve  Q.  Raise  the  tank  S  above  the  level  of  the  discharge 


GAS 


FIG.  74. — Sampling  tube  and  tanks. 

from  the  sampling  tube  and  fill  the  hose  N  and  also  the  sampling 
tube  with  water.  Introduce  the  sampling  tube  into  the  stack 
and  lower  tank  S,  allowing  the  water  to  flow  from  tank  R  to 
tank  S.  The  gases  will  thus  be  drawn  into  tank  R.  Again 
raise  tank  S  above  the  level  of  the  sampling  tube  and  allow  the 
water  to  return,  again  completely  filling  tank  R  and  hose  N. 


CHEMISTRY  OF  COMBUSTION  159 

Again  lower  tank  S  and  take  in  a  second  sample,  which  sample 
will  be  used  for  the  analysis.  The  first  sample  is  taken  into  the 
tanks  to  saturate  the  water  with  CO2,  so  that  when  the  second 
sample  is  taken  in,  the  water  will  not  absorb  any  more  of  the 
CO2,  but  will  leave  the  sample  just  as  it  was  in  the  flue.  Dis- 
connect hose  N  at  P  and  connect  tank  R  to  the  Orsat  apparatus 
(see  Fig.  73).  To  do  this,  attach  a  small  hose  to  the  capillary 
tube  C.  Open  the  valve  B  and  completely  fill  this  rubber  tube 
with  water  in  order  to  expel  the  air.  Connect  the  rubber  tube 
to  the  tank  R  at  the  valve  P,  lower  the  bottle  L,  and  open  the 
valve  P.  The  water  which  was  present  in  the  hose  connection 
will  be  drawn  back  to  the  measuring  tube  A  and  will  then  be 
followed  by  the  gas.  Allow  the  water  from  the  measuring  tube 
to  flow  into  the  bottle  L  until  approximately  100  c.c.  of  the  gas 
have  been  drawn  into  the  measuring  tube.  Valve  B  is  a  three- 
way  valve,  one  passage  communicating  with  the  atmosphere. 
Open  the  passage  to  the  atmosphere,  raise  the  bottle  L  and  expel 
all  of  the  gas  which  is  present  in  the  measuring  tube.  This  gas 
is  wasted  so  as  to  eliminate  any  error  which  might  arise  from  the 
fact  that  air  might  have  been  trapped  in  the  tube  connections. 
This  air  would  be  drawn  into  the  measuring  tube  when  the  first 
charge  of  gas  is  taken  into  the  apparatus.  Having  discharged 
all  of  the  gas,  place  valve  B  in  such  a  position  that  a  passage  is 
again  opened  into  the  tank  R  containing  the  gas  supply.  Again 
lower  bottle  L,  drawing  in  a  little  more  than  100  c.c.  of  gas. 
Now  close  valve  P  and  also  valve  B.  At  S  there  will  usually  be 
found  a  pinchcock  which  can  be  used  for  closing  the  connection  be- 
tween the  bottle  L  and  the  measuring  tube  A.  Bring  the  level  of 
the  liquid  in  the  bottle  L  even  with  the  level  of  the  water  in  the 
measuring  tube  A,  and  open  S.  This  will  insure  atmospheric 
pressure  in  the  measuring  tube  A.  If  there  are  more  than  100 
c.c.  of  gas  at  atmospheric  pressure,  raise  the  bottle  L,  compress 
the  gas  to  100  c.c.,  close  S,  and  open  valve  B  for  an  instant  to 
allow  the  surplus  to  pass  to  the  atmosphere.  Close  valve  JB, 
again  bring  the  level  of  the  water  in  the  bottle  L  even  with  the 
level  of  the  water  in  the  measuring  tube  A,  open  S  to  see  if  you 
have  100  c.c.  of  gas  at  atmospheric  pressure.  If  there  are  still 
more  than  100  c.c.,  repeat  the  operation.  Having  obtained  100 
c.c.  of  gas  at  atmospheric  pressure,  open  valve  M,  communicating 
with  pipette  D,  raise  the  bottle  L,  and  force  the  gas  from  the 
measuring  tube  into  the  pipette  D.  This  pipette  should  absorb 


160  STEAM  BOILERS 

the  carbonic  acid  which  is  present.  Allow  the  gas  to  remain  in 
pipette  D  for  4  or  5  minutes,  during  which  time  it  may  be  taken 
back  and  forth  two  or  three  times.  Now  draw  the  gas  back  into 
the  measuring  tube  A  and  in  doing  so  bring  the  level  of  the  liquid 
in  pipette  D  to  the  mark  which  will  be  on  the  capillary  tube  just 
below  M,  then  close  the  valve  M  of  pipette  D.  Bring  the  level 
of  the  water  in  bottle  L  even  with  the  level  of  the  water  in  the 
measuring  tube  A,  open  S,  thus  insuring  atmospheric  pressure 
in  the  measuring  tube.  The  reading  will  now  indicate  the 
number  of  c.c.  of  CO2  which  have  been  removed.  Repeat  the 
operation,  returning  the  gas  to  pipette  D  and  finally  take  the 
reading  at  atmospheric  pressure  as  before.  If  the  readings  are 
the  same,  it  is  evidence  of  the  fact  that  all  of  the  CO2  has  been 
removed  from  the  gas  and,  since  we  began  with  100  c.c.,  the 
number  of  c.c.  of  CO2  which  have  been  removed  will  also  be  the 
per  cent  of  C02  present  in  the  flue  gases. 

Having  removed  the  CO2,  open  the  valve  M  in  pipette  E  and 
repeat  the  operation,  using  pipette  E  for  the  absorption  of  the 
oxygen. 

After  removing  the  oxygen,  allow  the  gas  to  pass  into  pipette 
F  in  order  to  remove  the  CO. 

133.  Preparation  of  Reagents. — The  reagents  for  filling  the 
pipettes  D,  E,  and  F  may  be  prepared  as  follows: 

Caustic  Potash. — Dissolve  one  part  by  weight  of  caustic 
potash  made  by  the  lime  process  in  two  to  three  parts  of  distilled 
water.  The  caustic  potash  must  have  been  made  by  the  lime 
process,  as  that  made  by  the  alcohol  process  is  apt  to  give  rise  to 
errors  when  analyzing  the  flue  gas. 

Pyrogallol. — Take  about  5  grams  of  pyrogallic  acid  (which  is  a 
snow-like  powder)  and  wash  it  into  the  middle  pipette,  E,  with 
the  solution  of  caustic  potash  described  above. 

Cuprous  Chloride. — Make  up  a  stock  bottle  by  taking  2  oz.  of 
black  copper  oxide,  1  quart  of  commercial  hydrochloric  acid, 
and  1/2  Ib.  of  copper  wire,  putting  them  in  a  bottle  having  an 
air-tight  (rubber)  stopper.  Let  this  mixture  stand  until  clear, 
which  takes  about  10  days,  when  it  becomes  ready  for  use. 
Fill  the  pipette  from  stock  bottle  and  then  add  more  acid  to  the 
stock  bottle,  and,  if  it  seems  to  be  needed,  more  copper  wire  or 
copper  oxide.  In  this  way  a  constant  supply  may  be  kept  on 
hand.  The  cuprous  chloride  is  the  only  reagent  that  must  be 
prepared  previous  to  the  analysis. 


CHAPTER  XI 
FIRING 

134.  Methods  of  Firing. — It  is  very  hard  to  lay  down  any 
general  rules  for  firing,  as  different  kinds  of  coal  require  different 
treatments.     Coals  differ  very  much  in  their  character  and  the 
way  in  which  they  should  be  handled.     However,  there  are  a 
few  general  principles  which  will  apply  to  all  kinds  of  coal  and 
which  should  be  observed.     The  best  method  of  handling  the 
fire  with  any  particular  kind  of  fuel  is  best  found  by  experiment- 
ing with  it,  and  this  the  fireman  soon  learns  to  do.     There  are 
three  general  methods  of  firing,  known  respectively  as  the  coking 
method,  the  alternate  method,  and  the  spreading  method. 

135.  The  Coking  Method. — The  coking  method  should  be  used 
with  those  bituminous  coals  which  cake,  or  seem  to  melt  and  run 
together,  and  it  also  serves  well  for  coal  which  contains  a  large 
percentage  of  hydrocarbons,  even  if  the  coal  is  not  a  caking 
variety.     In  the  coking  method  of  firing,  the  fresh  coal  is  placed 
just  inside  the  furnace  door  and  allowed  to  remain  there  until 
the  heat  from  the  fire  drives  the  hydrocarbons  out  of  the  coal. 
As  the  hydrocarbons  are  driven  off,  a, considerable  quantity  of 
air  should  be  allowed  to  enter  through  the  damper  in  the  door. 
The  air  and  hydrocarbons  will  become  mixed  and,  as  they  have 
to  pass  over  the  hotter  portions  of  the  fire  in  order  to  reach  the 
chimney,   they  should  ignite   and  burn  completely  to   carbon 
dioxide  and  water.     After  the  hydrocarbons  are  driven  out  of 
the  coal,  the  remainder  is  in  the  form  of  coke,  wrhich  may  be 
pushed  back  into  the  hotter  portions  of  the  fire  where  complete 
combustion  is  readily  secured,  and  its  place  taken  by  a  fresh 
charge  of  coal.     Most  of  the  mechanical  stokers  in  use  to-day 
make  use  of  the  coking  method  of  firing. 

The  three  requirements  for  securing  complete  combustion  of 
the  coal  are:  (1)  to  have  a  sufficient  quantity  of  air;  (2)  to 
thoroughly  mix  the  air  with  the  hydrocarbon  gases  arising 
from  the  coal;  (3)  to  have  a  sufficiently  high  temperature  in 
the  furnace  to  cause  the  oxygen  in  the  air  to  unite  with  the 
hydrogen  and  carbon  compounds  in  the  gases, 

15  161 


162  STEAM  BOILERS 

These  three  requirements  are  very  well  met  in  the  coking 
method  of  firing.  The  hottest  portion  of  the  fire  is  near  the 
bridge  wall  where  the  coke  is  burning.  Being  in  this  position, 
the  hydrocarbon  gases  must  pass  through  a  region  of  very  high 
temperature  on  their  way  to  the  chimney.  The  hydrocarbons  are 
driven  off  near  the  front  of  the  fire  where  a  sufficient  quantity 
of  air  may  be  secured  through  the  door,  and  the  air  will  have 
sufficient  opportunity  to  become  thoroughly  mixed  with  the 
hydrocarbons  before  they  have  reached  the  hottest  part  of  the 
fire,  and  thus  they  will  have  no  opportunity  to  pass  out  of  the 
furnace  without  coming  in  contact  with  sufficient  oxygen. 

If  it  is  attempted  to  fire  a  caking  coal  by  spreading  it  over 
the  fire,  some  of  it  will,  of  course,  be  placed  back  near  the  bridge 
wall  and  the  hydrocarbons  from  this  portion  of  the  coal  will 
have  an  opportunity  to  pass  out  of  the  furnace  without  becoming- 
mixed  with  sufficient  air,  hence,  will  be  unburned  and  the  heat 
which  they  contain  will  be  lost.  The  coal  placed  on  other 
portions  of  the  fire  will  soon  melt  and  run  together,  forming  a 
pasty  mass  which  covers  the  entire  fuel  bed  and  serves  to  largely 
cut  off  the  supply  of  air  coming  up  through  the  grate.  It  will 
then  require  a  much  stronger  draft  to  burn  it  than  if  the  coking 
method  of  firing  had  been  used.  In  this  connection  it  may  also 
be  said  that  in  the  coking  method,  since  the  back  part  of  the  fire 
where  the  coke  is  being  burned  is  much  more  open  than  the 
front  part  where  the  coal  is  being  coked,  the  air  will  pass  more 
readily  through  the  back  part  of  the  fire,  and  for  this  reason  it 
should  be  kept  quite  thick.  A  disadvantage  of  this  method 
of  firing  is  that  the  fire  must  necessarily  be  stirred  up  considerably 
when  the  coke  is  pushed  back,  and  it  is  now  recognized  that  the 
fire  should  be  disturbed  as  little  as  possible. 

136.  The  Alternate  Method. — In  this  method,  fresh  coal  is 
fired  in  a  thin  layer  on  first  one  side  of  the  grate  and  then  on  the 
other.  The  volatile  matter  distilled  from  the  fresh  charge  on 
one  side  is  effectively  burned  by  the  air,  which  is  heated  when 
passing  through  the  other  side.  Even  in  this  case  some  of  the 
hydrocarbons  given  off  near  the  bridge  wall  are  likely  to  pass 
out  of  the  furnace  without  being  burned.  The  two  important 
stages  of  coal  burning  (combustion  of  the  volatile  matter  and 
burning  of  the  carbon)  occur  continuously  with  this  method  of 
firing.  This  makes  it  unnecessary  to  be  continually  altering 
the  air  supply  to  correspond  with  first  one  stage  of  the  combus- 


FIRING  163 

tion  and  then  with  the  other,  as  must  be  done  when  other  methods 
of  firing  are  used.  The  alternate  method  gives  excellent  results 
when  properly  carried  out,  but  it  is  necessary  to  make  provisions 
for  thoroughly  mixing  the  gases  from  the  two  sides  of  the  fire  if 
we  expect  to  burn  the  volatile  gases. 

In  this  method,  and  in  the  spreading  method  to  be  described 
next,  the  coal  should  be  thrown  exactly  where  it  is  wanted  and 
not  be  further  disturbed  by  the  poker  or  slice  bar,  except  when 
absolutely  necessary  to  clean  fires  or  break  up  clinkers. 

137.  Spreading  Method. — In  this  method  very  little  coal  is 
fired  at  a  time,  but  it  is  fired  often  and  each  charge  is  spread 
evenly  over  the  entire   fire  in   a  thin  layer.     The  spreading 
method  is  perhaps  used  more  extensively  in  hand  firing  than 
any  other,  probably  on  account  of  its  being  the  easiest.     This 
method  has  considerable  merit  when  the  boiler  is  set  high  above 
the  grate  so  the  gases  may  rise  straight  up  from  the  coal,  thus 
having  an  opportunity  to  burn  before  passing  out  of  the  com- 
bustion chamber.     It  is  true  that  by  the  spreading  method  of 
firing  some  of  the  volatile  matter  rising  from  the  coal  near  the 
back  end  of  the  grate  will  pass  over  the  bridge  wall  without 
being  burned,  but  the  loss  from  this  source  will  be  small  if  the 
coal  is  spread  in  a  thin  layer  and  if  a  hot  fire  is  maintained. 
This  method,  in  common  with  the  alternate  method,  has  the 
advantage  that  the  fire  need  be  disturbed  but  little.     Sometimes 
a  modified  spreading  method  is  used  whereby  the  coal  is  fired 
in  patches,  covering  only  a  portion  of  the  grate.     It  appears, 
however,   that  this   modification  has   no   advantage   over  the 
ordinary  spreading  method.' 

138.  Rules  for  Hand  Firing. — The  following  excellent  rules 
have  been  formulated  by  the   Coal  Stoking  and  Anti-smoke 
Committee  of  the  Illinois  Coal  Operators  Association  for  the 
hand  firing  of  Illinois  and  Indiana  coals. 

(1)  Break  all  lumps,  and  do  not  throw  any  in  the  furnace 
which   are  larger  than  your  fist.     The  reason  for  this  is  that 
large  lumps  do  not  ignite  promptly  and  their  presence  also 
causes  holes  to  form  in  the  fire,  which  allow  the  passage  of  too 
much  air. 

(2)  Keep  the  ash  pits  bright  at  all  times.  If  they  become  dark 
this  is  evidence  that  the  fire  is  getting  dirty  and  needs  cleaning, 
which,  if  not  done,  will  cause  imperfect  combustion  and  smoke. 
If  the  furnace  is  equipped  with  a  shaking  grate,  it  should  be 


164  STEAM  BOILERS 

operated  often  enough  to  prevent  any  accumulation  of  ashes  in 
the  fire.  Do  not  allow  ashes  to  collect  in  the  ash  pits,  as  they 
not  only  shut  off  the  air  supply,  but  may  cause  the  grate  to  be 
burned. 

(3)  In  firing  do  not  land  the  coal  all  in  one  heap  but,  as  it 
leaves  the  shovel,  spread  it  over  as  wide  a  space  as  possible.     A 
little  practice  will  enable  one  to  catch  the  proper  motion  to  give 
the  shovel  in  order  to  make  the  coal  spread  properly. 

(4)  Place  the  fresh  coal  from  the  bridge  wall  forward  to  the 
dead  plate  and  do  not  add  more  than  three  or  four  shovels  at  a 
charge.     If  this  amount  makes  smoke  it  should  be  reduced  till 
smoke  ceases,  which  means,  of  course,  that  firing  will  be  at  more 
frequent  intervals  than  formerly  to  keep  up  steam.     This  rule 
applies  in  cases  where  the  boiler  is  worked  at  a  large  capacity. 
In  such  instances,   however,   where   a  small   capacity   only  is 
required,  firing  by  the  coking  method,  wherein  the  fresh  coal  is 
placed  at  the  front  of  the  fire,  and  pushed  back  and  leveled  when 
it  has  become  coked,  is  the  best. 

(5)  Fire  one  side  of  the  furnace  at  a  time  so  that  the  other  side 
containing  a  bright  fire  will  ignite  the  volatile  gases  from  the 
fresh  charge. 

(6)  Do  not  allow  the  fire  to  burn  down  dull  before  charging. 
If  this  is  done,  it  will  not  only  result  in  a  smoky  chimney,  but  an 
irregular  steam  pressure. 

(7)  Do  not  allow  holes  to  form  in  the  fire.     Should  one  form, 
fill  it  by  leveling  and  not  by  a  scoop  full  of  coal.     Keep  the  fire 
even  and  level  at  all  times.     As  far  as  possible  level  the  fire 
after  the  coal  has  become  coked. 

(8)  Carry  as  thick  a  fire  as  the  draft  will  allow,  but  in  deciding 
on  the  proper  thickness,  judgment  must  be  exercised.     If  the 
draft  is  weak,  a  thin  fire  will  be  in  order,  but  if  strong,  a  thicker 
fire  should  be  carried. 

(9)  Regulate  the  draft  by  the  bottom  or  ash  pit  doors  and  not 
by  the  stack  dampers,  because,  when  the  stack  damper  is  used, 
it  tends  to  produce  a  smoky  chimney  as  it  reduces  the  draft, 
while  the  closing  of  the  ash  pit  door  diminishes  the  capacity  to 
burn  coal.     If  strict  attention  is  given  to  firing  according  to 
demand  for  steam,  there  will  be  no  occasion  to  have  recourse  to 
the  dampers  except  when  there  is  a  sudden  interruption  in  the 
amount  of  steam  being  used. 

(10)  A  good  general  rule  is  to  fire  little  and  often,  according 


FIRING  165 

to  steam  demands,  rather  than  heavy  and  seldom.  The  former 
means  economy  in  fuel  and  a  clean  chimney,  while  the  latter 
signifies  extravagance  in  fuel  and  a  smoky  chimney. 

139.  Smoke   Prevention. — The   prevention   of    smoke    means 
more  economical  operation  of  the  furnace,  provided  the  absence 
of  smoke  is  secured  by  the  complete  combustion  of  the  coal  and 
without  too  great  excess  of  air.     However,  the  absence  of  smoke 
should  not  be  taken  as  conclusive  proof  that  the  furnace  is  being- 
operated  in  the  most  economical  manner.     If  a  very  great  excess 
of  air  is  admitted  to  the  furnace,  the  smoke  may  be  so  diluted  as 
to  become  almost  invisible,  but  the  efficiency  will  be  low.     Under 
such  conditions,  not  only  is  the  furnace  temperature  lowered,  but 
also  a  large  amount  of  heat  is  wasted  in  raising  the  temperature  of 
the  excess  air.     If  an  analysis  of  the  flue  gas  shows  more  than 
100  per  cent  excess  air,  steps  should  be  taken  at  once  to  prevent 
so  much  air  entering  the  furnace. 

Smoke  is  the  product  of  volatile  matter  that  has  not  been 
burned.  To  burn  the  volatile  matter  of  a  coal  we  must  have 
three  things :  first,  a  supply  of  oxygen  sufficient  for  the  volatile 
matter;  second,  a  thorough  mixture  of  this  air  and  volatile 
matter;  third,  a  sufficient  temperature  after  mixing  to  cause  and 
maintain  combustion. 

Fresh  coal  requires  more  air  than  coal  that  has  been  coked. 
Therefore,  either  more  air  should  be  supplied  just  after  firing,  or 
the  firing  should  be  continuous  so  as  to  constantly  use  the  same 
proportion  of  air. 

The  boiler  should  not  be  too  close  to  the  fire.  The  volatile 
gases  are  often  chilled  by  the  bottom  and  the  tubes  of  a  boiler 
so  that  they  cease  burning.  For  coals  containing  much  volatile 
matter,  a  Dutch  oven  furnace  is  highly  desirable  as  it  permits 
of  thorough  mixing  of  air  and  volatile  matter  and  maintains  a 
high  furnace  temperature.  Automatic  stokers  naturally  offer  the 
best  method  of  smoke  prevention  as  they  supply  the  coal  con- 
tinuously and  the  air  as  well  as  the  depth  of  fire  carried  can  be 
regulated. 

140.  Mechanical  Stokers. — These   may  be   divided  into  two 
general  classes:  (1)  overfeed  and  (2)  underfeed.     The  first  feeds 
the  coal  above  the  fire  and  the  second  feeds  it  below,  then  up- 
ward, until  it  overflows  out  over  the  grates. 

There  are  three  kinds  of  overfeed  stokers  in  use.  In  one,  the 
coal  is  carried  on  horizontal  or  slightly  inclined  grate  bars,  and 


166 


STEAM  BOILERS 


the  individual  bars  are  given  a  motion  by  which  the  coal  is  grad- 
ually advanced  along  the  grates  toward  the  bridge  wall.  In 
another,  the  grates  are  steeply  inclined,  and  the  fuel  is  pushed 
onto  the  upper  ends,  whence  is  slides  down  slowly  toward  the  ash 
pit,  being  burned  on  its  way  down.  Still  another  kind  includes 
chain  grates,  in  which  the  entire  grate  is  an  endless  chain  of 
short  bars.  The  motion  is  from  the  fuel  hopper,  in  front  of  the 
boiler,  back  toward  the  bridge  wall,  at  which  point  the  grate 
passes  over  a  sprocket  and  returns  through  the  ash  pit. 


DETAILS   OF    WILKINSON    STOKER 

FIG.  75.     ' 

Underfeed  stokers  feed  into  a  trough-shaped  retort  below  the 
grates,  and  the  fuel  gradually  overflows  out  and  over  the  grates 
along  each  side  of  the  retort.  It  undergoes  a  coking  process  in 
the  retort  and  should  be  free  from  all  volatile  matter  when  the 
grates  are  reached.  Air  for  combustion  is  supplied  through 
openings  along  the  edges  of  the  retort.  Some  of  these  stokers 
operate  intermittently  by  means  of  a  plunger;  others  feed 
continuously  through  a  screw  motion.  Forced  draft  is  most 
often  used. 

141.  The  Wilkinson  Stoker.— Fig.  75  shows  the  details  of  a 
Wilkinson  mechanical  stoker  which  is  a  representative  of  the 


FIRING  167 

front  feed  slightly  inclined  type.  In  this  stoker  the  coal  is  fed 
from  a  hopper  onto  inclined  grate  bars.  The  grate  bars  are 
made  in  one  piece  with  the  upper  edge  corrugated  in  the  form 
of  steps.  Each  bar  is  fastened  near  its  upper  end  to  a  link  which 
connects  it  to  a  toggle  shaft  from  which  it  takes  its  motion.  The 
links  have  a  reciprocating  motion,  and  alternate  bars  are  so 
connected  to  the  toggle  shaft  as  to  be  out  of  phase  with  the  others, 
thus  giving  the  bars  a  sawing  motion  which  serves  to  feed  the 
coal  forward  and  downward.  The  toggle  shaft  is  operated  by  a 
hydraulic  motor  which  receives  its  supply  of  water  from  a  small 
independent  pump.  The  water  is  used  over  and  over  in  the 
motor  and  pump.  The  grate  bars  are  hollow  and  each  one  has 
a  small  steam  jet  in  it  by  which  a  small  amount  of  steam  is 
blown  through  small  openings  in  the  upper  edge  of  the  grate 
bars  and  through  the  fires.  This  serves  not  only  to  prevent 
clinkering,  but  also  draws  air  into  the  fire. 

Part  of  the  ash  formed  during  combustion  sifts  through  the 
grate  bars.  The  remainder,  together  with  the  clinker,  moves 
down  the  inclined  grate  bars  to  the  ash  table  at  the  bottom.  The 
motion  of  the  lower  ends  of  the  grate  bars  pushes  the  ashes  and 
clinkers  onto  a  dumping  plate  which  may  be  lowered,  thus 
discharging  them  into  the  ash  pit. 

142.  The  Roney  Stoker. — This  stoker,  illustrated  in  Fig.  76,  is 
a  good  representative  of  the  steeply  inclined  front  feed  stoker. 
Unlike  the  Wilkinson  stoker,  it  has  the  grate  bars  placed  across 
the  furnace  and  each  one  forms  a  step  just  below  the  one  above. 
The  bars  are  T-shaped  in  section  and  are  pivoted  near  their  lower 
ends.  The  lower  ends  of  the  bars  rest  in  slots  cut  in  a  rocker  bar, 
from  which  they  obtain  their  rocking  motion.  The  rocker  bar 
is  given  a  reciprocating  motion  through  a  rod,  which  derives  its 
motion  from  a  shaft  passing  in  front  of  the  stoker  and  operated 
by  a  small  steam  engine.  The  coal  is  fed  from  a  hopper  to  the 
dead  plate  just  below,  from  which  it  is  pushed  onto  the  grate 
bars  by  a  pusher  plate  sliding  back  and  forth  over  the  dead  plate. 
The  grate  bars  oscillate  through  an  angle  of  about  30°,  alternately 
assuming  a  horizontal  and  an  inclined  position,  thus  gradually 
feeding  the  coal  down  the  incline.  The  stoker  normally  operates 
at  about  10  strokes  per  minute  and  the  rate  of  feeding  the  coal 
is  regulated  by  adjusting  a  hand  wheel  which  controls  the 
amplitude  of  the  motion  of  the  pusher  plate.  By  the  time  the 
coal  reaches  the  bottom  of  the  grates,  it  is  completely  burned, 


168  STEAM  BOILERS 

and  the  clinkers  and  ash  may  be  dumped  into  the  ash  pit  by 
means  of  a  dumping  grate  provided  for  this  purpose. 

143.  The  Murphy  Stoker.— The  Murphy  Stoker  shown  in  Figs. 
77  and  78,  represents  another  style  of  steeply  inclined  stoker. 
This  one  differs  from  the  other  in  that  it  has  two  sets  of  grates, 
one  placed  along  each  side  of  and  extending  the  depth  of  the 
furnace.  This  apparatus  is,  in  effect,  a  Dutch  oven  with  an 


FIG.   76. — Roney  stoker. 

automatic  feeding  and  stoking  device.  Coal  is  fed  from  hoppers 
placed  along  both  sides  of  the  furnace.  From  the  hopper,  the 
coal  runs  onto  a  coking  plate  from  which  it  is  pushed  by  a 
reciprocating  stoker  box.  The  grate  bars  are  inclined  toward 
the  center  of  the  furnace,  and  are  pivoted  near  their  upper  ends. 
Only  the  alternate  bars  are  movable,  and  these  are  connected 
to  a  shaft  in  the  middle  of  the  furnace  and  at  the  bottom  in 
such  manner  as  to  give  them  a  motion  alternately  above  and 
below  the  surface  of  the  stationary  grates.  This  serves  to  feed 
the  coal  down  the  incline.  A  hollow  shaft  with  strong  teeth 
on  the  outside  is  placed  in  the  bottom  of  the  stoker  for  grinding 


FIRING 


169 


FIG.  77. — Murphy  stoker. 


FIG.  78. — Rear  view  of  Murphy  stoker. 


170 


STEAM  BOILERS 


up  the  clinkers.  Cold  air  passes  through  this  shaft  and  prevents 
it  from  becoming  overheated.  Air  for  burning  the  volatile  matter 
is  fed  through  flues  in  the  stoker  box,  where  it  is  warmed  before 
entering  the  furnace.  The  motion  of  the  stoker  box  is  adjustable 
to  control  the  rate  of  feeding.  A  rear  view  of  this  stoker,  showing 
a  double  arch  construction,  is  illustrated  in  Fig.  78.  This  stoker 
can  be  operated  without  smoke  at  all  loads,  and  is  particularly 
well  adapted  for  operation  at  small  loads  as  the  ashes  may  be 
allowed  to  collect  and  cover  up  a  portion  of  the  grates,  thus 
reducing  the  effective  grate  area. 

144.  The  Jones  Underfeed  Stoker. — The  Jones  Stoker  shown  in 
longitudinal  section  in  Fig.  79  and  in  cross-section  in  Fig.  80  is 


FIG.  79. — Longitudinal  section  of  Jones  underfeed  stoker. 


of  the  underfeed  type.  This  stoker  is  very  simple  in  construction 
and  has  but  few  moving  parts.  It  consists  of  a  retort,  which  is 
placed  inside  the  furnace,  and  of  a  feeding  mechanism  placed 
outside.  The  retort  is  trough-shaped  and  along  each  side  at  the 
upper  edge  is  placed  the  tuyeres  for  admitting  air  under  the  bed 
of  coal.  The  feeding  mechanism  consists  of  two  cylinders  fitted 
with  pistons  placed  one  in  front  of  the  other.  The  two  pistons 
are  placed  on  a  single  piston  rod,  and  therefore  move  together. 
The  outer  or  actuating  piston  is  acted  upon  by  live  steam  from 
the  boiler  and  as  this  piston  moves  in,  it  pushes  the  other  piston 
or  ram  which  in  turn  pushes  some  coal  from  the  hopper  into  the 
retort.  As  the  ram  forces  more  coal  into  the  hopper,  some  of 
that  which  was  already  there  is  forced  upward  toward  the  top 
and  in  this  way  the  bed  of  coals  assumes  the  form  of  a  ridge 


FIRING 


171 


extending  down  the  middle  of  the  furnace,  as  seen  in  Fig.  80, 
being  thick  in  the  center  and  thin  along  the  edges.  In  order  to 
prevent  the  coal  from  heaping  up  too  much  in  front  of  the  furnace, 
a  couple  of  pusher  blocks  connected  to  the  piston  rod  are  placed 
in  the  bottom  of  the  retort,  which,  by  their  motion  to  and  fro, 
serve  to  level  the  fire  somewhat. 


»***.•«'  »**• 


FIG.  80. — Cross-section  of  Jones  underfeed  stoker. 

A  fan  is  used  to  supply  air  beneath  the  stoker  through  a  duct 
as  shown  in  Fig.  80.  From  here  the  air  passes  through  the  tuyeres 
on  each  side  of  the  retort  and  up  through  the  fire.  The  fan  is 
run  by  a  steam  engine  or  electric  motor  whose  speed  is  con- 
trolled automatically  by  the  steam  pressure.  The  frequency 
of  strokes  of  the  feeding  ram  is  also  controlled  automatically 
by  the  steam  pressure.  By  this  method  of  control  the  amount 
of  air  supplied  to  the  furnace  is  regulated  to  suit  the  required 


172  STEAM  BOILERS 

rate  of  combustion  and  there  is  no  danger  of  excess  air  being 
supplied. 

In  the  underfeed  stoker  just  described,  the  ash  and  clinker 
are  worked  to  the  top  of  the  fire  by  the  upward  motion  of  the 
coal.  From  here  they  gradually  move  down  the  sloping  sides 
of  the  fuel  bed  to  the  sides  of  the  retort,  which  are  flat.  Cleaning- 
doors  are  provided  at  each  side  of  the  furnace  through  which 
the  ashes  and  clinkers  may  be  removed  at  intervals. 

In  the  underfeed  system  of  stoking,  the  hottest  part  of  the 
fire  is  at  the  top  of  the  fuel  bed,  while  the  fuel  in  the  bottom  of 
the  retort  is  cool.  As  the  fuel  is  fed  upward,  it  becomes  heated 
and  the  volatile  matter  is  driven  out.  This  must  pass  up 
through  the  hotter  part  of  the  fire  above,  where,  the  chances 
are,  it  will  be  completely  burned  before  it  passes  out  of  the 
furnace.  This  principle  of  stoking  permits  very  low  grade  coals 
being  burned  with  a  minimum  of  smoke,  and  also  permits  the 
metal  parts  of  the  boiler  being  set  directly  over  the  furnace  with- 
out danger  of  the  gases  being  cooled  before  they  are  burned. 

145.  The  Taylor  Gravity  Underfeed  Stoker.— The  Taylor 
stoker,  illustrated  in  Figs.  81  and  82,  is  a  combination  of  the 


FIG.  81. — Rear  view  of  Taylor  gravity  underfeed  stoker. 

two  types  of  stokers  just  described,  having  an  inclined  grate 
and  at  the  same  time  being  underfed.  This  stoker,  like  others 
of  the  underfeed  type,  requires  a  strong  draft  to  force  the  air 
through  the  thick  fuel  bed,  and  this  draft  is  best  furnished  by  a 


FIRING 


173 


fan.  The  inclined  grate  bars  are  all  stationary  and  are  hollow, 
having  openings  on  their  faces  as  shown  in  the  back  view  of  the 
stoker,  Fig.  82.  These  hollow  grate  bars  are  connected  to  a 
common  air  chamber  underneath  the  stoker,  which  chamber  is 
supplied  with  air  through  a  duct,  as  illustrated  in  Fig.  81. 

The  feeding  mechanism  consists  of  two  sets  of  rams,  one  near 
the  top  of  and  between  the  grate  bars,  and  the  other  immediately 
below,  both  sets  being  operated  from  a  crank  shaft  on  the  out- 


FIG.  82. — Longitudinal  section  of  Taylor  gravity  underfeed  stoker. 

side  of  the  stoker.  The  relative  positions  of  the  rams  may  be 
seen  from  Fig.  82.  The  top  ram  is  located  in  the  bottom  of  the 
coal  hopper,  and  is  the  one  which  really  does  the  feeding  of  fresh 
coal,  while  the  other  ram  serves  to-  keep  the  coal  moving  down 
the  grate  bars,  thus  securing  a  more  uniform  fire  over  the  whole 
fuel  bed. 

The  ashes  and  "clinkers  move  toward  the  bottom  of  the  grate 
bars  as  the  coal  is  burned,  and  finally  collect  on  the  dumping 
plates  at  the  bottom,  from  which  they  may  be  dumped  into  the 


174 


STEAM  BOILERS 


ash  pit  by  means  of  hand  levers,  which  extend  to  the  front  of 
the  stoker. 

In  the  Taylor  stoker,  the  air  supply  and  rate  of  feeding  coal 
are  controlled  automatically  by  the  steam  pressure,  thus  insuring 
at  all  times  the  proper  amount  of  air  to  burn  the  coal.  Besides 
the  advantages  common  to  all  underfeed  stokers,  the  Taylor  has 
the  further  advantage  that  the  fuel  bed  extends  entirely  across 
the  furnace,  thus  utilizing  all  the  space  in  the  furnace  and 
giving  maximum  capacity  for  minimum  space. 

146.  Chain  Grates. — Fig.  83  represents  the  Green  chain  grate 
as  applied  to  a  water  tube  boiler  with  fire-clay  tiling  on  the 
lower  course  of  tubes.  It  consists  of  an  endless  chain  of  grate 


FIG.  83. — Green  chain  grate  stoker. 

bars  mounted  on  a  frame,  with  provision  for  the  uniform  feeding 
of  the  fuel.  The  driving  mechanism  consists  of  a  train  of  gears 
operated  from  a  line  shaft,  the  gears  being  actuated  by  ratchet 
and  pawls.  Fuel  is  fed  into  the  front  end  from  a  hopper  provided 
with  an  adjustable  feed  gate  for  levelling  and  regulating  the 
depth  of  the  fuel  bed.  The  entire  stoker  is  mounted  on  wheels 
which  run  on  a  track,  thus  permitting  the  easy  removal  of  the 
stoker  for  inspection  or  repairs.  The  thickness  of  the  fuel  bed 
and  the  speed  of  the  grates  are  so  regulated  that  the  fuel  is  com- 
pletely consumed  by  the  time  it  reaches  the  rear  of  the  furnace, 
and  only  the  ashes  and  clinkers  are  dumped  off  into  the  ash  pit. 
The  combination  of  a  chain  grate  with  an  inclined  ignition  arch, 


FIRING  175 

and  with  the  lower  course  of  tubes  covered  with  fire  tiles  as 
shown  in  Fig.  83,  makes  an  excellent  smokeless  furnace,  though 
the  depth  of  fuel  and  speed  of  the  stoker  must  be  closely  regu- 
lated if  it  is  to  accomplish  its  purpose.  With  chain  grate  stokers 
there  is  apt  to  be  considerable  leakage  of  air  past  the  sides  of  the 
grate,  through  the  end,  which  is  covered  with  ashes,  and  through 
the  fuel  in  the  hopper  but,  by  careful  construction,  leakage  from 
these  sources  may  be  largely  overcome. 

147.  Advantages  and  Disadvantages  of  Stokers. — One  of  the 
most  apparent  advantages  in  the  use  of  mechanical  stokers  is  the 
saving  in  the  fire-room  labor.  This  is  particularly  true  in  large 
plants  and  where  coal-handling  machinery  is  used.  Stokers 
may  save  as  much  as  30  to  40  per  cent  of  the  labor  in  large  plants, 
that  is,  plants  using  over  200  tons  of  coal  per  week.  In  plants  of 
medium  size,  those  using  from  50  to  150  tons  of  coal  per  week, 
the  saving  in  labor  may  amount  to  from  20  to  30  per  cent.  In 
small  plants  there  is  not  likely  to  be  a  saving  in  labor. 

In  a  large  plant,  stokers  will  be  advisable  if  they  permit  the 
use  of  a  cheaper  grade  of  fuel  than  could  be  used  with  hand  firing, 
but  it  should  be  ascertained  that  the  cheaper  fuel  could  not  be 
used  without  the  stoker.  Usually  a  stoker  can  be  made  to  burn 
a  lower  grade  of  fuel  than  can  be  used  with  hand  firing,  since 
it  carries  a  cleaner  fire,  the  coal  is  fed  more  uniformly,  and  the 
amount  of  air  required  for  combustion  is  supplied  at  a  more 
constant  rate. 

Even  if  no  saving  can  be  effected  by  using  a  cheaper  grade 
of  fuel,  it  may  still  be  advisable  to  use  a  stoker,  to  lessen  the 
smoke  if  a  cheap  grade  of  fuel  is  being  used.  It  is  difficult  to 
prevent  smoke  when  such  fuels  are  hand  fired.  The  amount 
of  smoke  given  off  by  a  furnace  may  be  greatly  reduced  or  even 
entirely  eliminated  by  the  use  of  a  stoker  of  proper  design,  when 
operated  according  to  the  principles  upon  which  it  was  intended 
to  be  operated.  However,  in  practice,  stokers  are  not  always 
operated  to  the  best  advantage,  and  we  sometimes  see  a  stoker- 
fired  furnace  giving  off  quite  as  much  smoke  as  a  hand-fired  one. 

The  grate  area  of  a  stoker  is  usually  less  than  that  of  a 
hand-fired  grate  for  the  same  furnace,  but  since  the  motion  of  the 
stoker  maintains  a  cleaner  fire  by  continuously  disturbing  the 
film  of  ash  formed  by  the  burning  coal,  the  rate  of  combustion 
per  square  foot  of  grate  is  increased  sufficiently  to  make  up  for 
the  reduction  in  grate  area. 


176  STEAM  BOILERS 

It  is  often  claimed  that  the  use  of  stokers  increases  the  evap- 
oration per  pound  of  coal.  This  will  depend  largely  upon  the 
design  of  the  stoker  and  the  way  in  which  it  is  handled.  In 
this  connection  it  should  be  remembered  that  all  fuel  .used  to 
operate  the  stoker  or  steam  jets,  if  there  be  any,  should  be 
charged  against  it. 

Unless  the  fireman  be  expert,  hand  firing  may  occasion  a 
loss  as  compared  with  a  stoker,  for  the  following  reason.  There 
is  a  certain  supply  of  air  per  pound  of  coal  which  gives  best 
results,  too  much  or  too  little  resulting  in  a  loss.  If  the  firing  be 
continuous,  as  in  a  stoker,  the  supply  of  air  may  be  adjusted 
to  suit  the  rate  of  firing.  If  the  firing  be  intermittent,  as  in 
hand  firing,  the  air  supply  is  first  too  small  and  then  too  large, 
and  a  loss  results.  The  more  intermittent  the  firing,  the  greater 
will  be  the  variation  from  the  proper  air  supply  and  the  greater 
will  be  the  loss.  The  proper  air  supply  per  pound  of  coal  shows 
a  greater  tendency  to  \ary  with  soft  coals  than  with  hard  coals, 
hence,  with  soft  coals,  it  is  more  difficult  to  obtain  good  results 
with  hand  firing  than  with  the  use  of  a  stoker. 

After  the  best  type  of  stoker  to  handle  a  particular  grade  of 
coal  has  been  chosen,  then  the  best  stoker  will  be  that  one 
which  is  least  complicated  and  whose  details  are  designed 
according  to  good  mechanical  principles. 

148.-  Oil  Burning. — The  use  of  crude  oil  as  a  fuel  under  power 
boilers  has  attained  considerable  prominence  within  the  last 
few  years.  Railroads  have  been  the  most  prominent  users  of 
this  fuel,  and  particularly  those  railroads  which  run  near  the 
oil  fields. 

In  order  to  burn  oil  successfully,  it  is  necessary  to  have  a 
suitable  spraying  device  for  the  oil  and  a  furnace  constructed 
especially  for  oil  burning.  The  spraying  devices  used  most 
commonly  in  this  country  are  either  of  the  inside  or  outside 
mixing  types.  While  there  are  several  good  burners  of  each  of 
these  types  on  the  market,  only  one  of  each  type  will  be  de- 
scribed, as  this  will  be  sufficient  to  illustrate  the  principles  of  their 
construction.  In  all  of  these  burners  the  oil  is  mixed  with 
either  steam  or  compressed  air,  which  serves  to  spray  it  and 
force  it  into  the  furnace. 

Fig.  84  shows  a  Booth  burner  which  is  of  the  outside  mixing 
type.  This  burner  consists  of  two  pipes,  one  above  the  other, 
the  spraying  ends  of  the  pipes  being  flattened  out  until  the 


FIRING 


177 


mouth  is  a  thin  slit.  The  oil  passing  through  the  upper  pipe  flows 
through  the  slit  and  falls  upon  a  jet  of  steam  issuing  from  the 
lower  pipe,  which  atomizes  and  forces  it  into  the  furnace.  A 
feature  of  this  apparatus  is  its  simplicity  and  freedom  from 
clogging. 


BOOTH   OIL  BURNER 


FIG.  84. 

The  Hammel  burner,  which  is  of  the  inside  mixing  type,  is 
shown  in  Fig.  85.  Oil  enters  the  burner  under  pressure  and 
flows  through  opening  D  to  the  mouth  of  the  burner,,  where  it  is 
atomized  by  the  steam  jets  issuing  from  the  slots  G,  H,  and  / 
surrounding  the  oil  opening  D.  The  plate  K  serves  to  flatten 


HAMMEL  OIL  BUPNER 

FIG.  85. 

out  and  direct  the  spray.     This  plate  is  removable  and  is  easily 
replaced  when  worn  out  or  burned. 

The  construction  of  a  furnace  for  the  use  of  oil  under  a  water- 
tube  boiler  is  illustrated  in  Fig.  86.  The  bottom  of  the  furnace 
consists  of  a  double  air  passage  which  allows  the  air  to  be  heated 
before  it  enters  the  furnace.  The  jet  of  oil  and  steam,  or  of  oil  and 

16 


178 


STEAM  BOILERS 


compressed  air,  impinges  against  the  stack  of  loosely  piled  fire 
brick  placed  just  in  front  of  the  bridge  wall.  These  brick  serve 
the  double  purpose  of  storing  heat  and  of  projecting  the  lining 
of  the  bridge  wall.  Being  piled  loosely,  they  may  be  readily 
replaced  when  they  become  burned. 

Some  years  ago  the  U.  S.  Naval  Liquid  Fuel  Board  conducted 
an  elaborate  series  of  experiments  upon  liquid  fuel  and  among 
its  conclusions  were: 

(1)  That  oil  can  be  burned  in  a  very  uniform  manner. 

(2)  That  the  evaporation  efficiency  of  nearly  every  kind  of 
oil  per  pound  of  combustible  is  probably  the  same. 

(3)  That  a  marine  steam  generator  can  be  forced  to  as  high 
degree  with  oil  as  with  coal. 


FIG.  86. — Furnace  fitted  for  burning  oil. 

(4)  That  no  ill  effects  were  shown  upon  the  boiler. 

(5)  That  the  firemen  were  disposed  to  favor  oil. 

(6)  That  the  air  requisite  for  combustion  should  be  heated, 
if  possible,  before  entering  the  furnace. 

(7)  That  the  oil  should  be  heated  so  that  it  can  be  atomized 
more  readily. 

(8)  That  when  using  steam,  higher  pressures  are  more  advan- 
tageous than  lower  pressures  for  atomizing  the  oil. 

(9)  That  under  heavy  forced  draft,   and  particularly  when 
steam  was  used,  it  was  not  possible  to  prevent  smoke. 

(10)  That  the  efficiency  of  the  oil  fuel  plant  will  be  greatly 
dependent   upon  the   general   character  of  the   installation   of 
auxiliaries  and  fittings. 


CHAPTER  XII 
THE  SMOKELESS  COMBUSTION  OF  COAL 

149.  The  Smoke  Problem. — There  are  two  phases  or  sides 
to  the  smoke  question;  that  of  the  proprietor  who  is  responsible 
for  the  smoke  and  that  of  the  community  which  is  interested 
in  the  prevention  of  the  smoke.  For  many  years  these  two 
interests  seemed  to  be  antagonistic  but  more  recently  they  have 
come  to  recognize  a  community  of  interests.  It  is  not  intended 
to  deal  in  this  course  with  the  civic  problem  of  smoke  except 
to  give  a  few  interesting  figures.  According  to  the  smoke  in- 
spector of  Chicago,  the  annual  loss  in  ruined  merchandise, 
increased  laundry  bills,  and  in  other  ways,  due  to  smoke,  amounts 
to  $50,000,000  for  Chicago  alone.  Since  one-third  of  our  popu- 
lation lives  in  cities,  the  U.  S.  Geological  Survey  has  reasoned 
from  this  that  the  annual  loss  to  the  country  is  about  $600,000,000 
or  about  $6  per  individual.  Whether  these  figures  are  correct 
or  not  there  is  doubtless  a  considerable  loss  due  to  the  smoke 
produced  by  our  factories  and  power  stations.  At  first  glance 
it  might  appear  that  the  factory  proprietor  is  not  interested  in 
smoke  prevention  to  any  greater  extent  than  that  of  his  own  $6 
share  in  the  annual  loss.  But  this  $600,000,000  expenditure 
decreases  the  purchasing  power  of  the  people  by  that  same 
amount  yearly  and  thus  what  we  call  the  prosperity  of  the 
country  is  correspondingly  diminished.  It  is  true  that  most  of 
the  money  so  expended  stays  in  our  country  but  the  expenditure 
of  this  money  whether  within  or  without  the  country,  since  it  is 
not  in  exchange  for  something  else  of  permanent  value,  has  as 
evil  an  effect  on  our  prosperity  as  if  the  nation  were  carrying 
on  a  continual  war  at  an  expense  of  $600,000,000  yearly.  The 
business  of  each  factory  or  power  station  is,  therefore,  dimin- 
ished in  the  proportion  which  this  $600,000,000  bears  to  the 
total  business  of  the  country. 

But  since  these  facts  do  not  seem  sufficient  to  influence 
the  industrial  interests  of  the  nation,  it  becomes  necessary  to 
demonstrate  the  economy  of  smoke  prevention  in  another  way. 

179 


180  STEAM  BOILERS 

The  issuing  of  black  smoke  from  a  chimney  is  invariably  a  sign 
that  the  best  results  are  not  being  obtained  from  the  coal  burned. 
When  it  is  considered  that  the  coal  bill  of  the  average  factory, 
if  saved,  would  pay  a  6  per  cent  dividend  on  the  capital  stock, 
it  is  seen  that  what  the  factory  manager  can  save  by  proper 
attention  to  the  generation  of  his  power  will  go  a  considerable 
way  toward  making  up  the  dividends  which  he  is  expected  to 
earn. 

Geologists  figure  that,  at  the  present  rate  of  increase  in  our 
coal  consumption,  our  visible  coal  supply  will  last  only  about 
200  years  longer.  This  fact  may  also  have  little  effect  on  the 
factory  manager  until  he  is  made  to  realize  that  this  approaching 
shortage  in  coal  is  already  having  its  effect  on  the  price  of  coal. 
This  can  be  readily  appreciated  when  we  see  shallow  veins  of 
coal  being  mined  that  a  few  years  ago  could  not  have  been 
worked  at  a  profit. 

It  is  not  the  unburned  carbon  in  smoke  that  is  the  great 
loss,  since  this  carbon  or  soot  in  the  blackest  smoke  is  less  than 
1  per  cent  of  the  total  carbon  in  the  coal,  but  in  general  the 
presence  of  soot  indicates  also  the  presence  of  other  combusti- 
ble matter  that  is  not  visible  but  is  being  wasted  in  amounts  of 
from  3  to  10  per  cent  of  the  available  combustible.  Further- 
more, the  heat  which  is  liberated  in  the  furnace  may  not  be 
so  liberated  as  to  give  its  greatest  possible  percentage  to  the 
water  in  the  boiler.  Understanding  and  observing  the  princi- 
ples of  combustion  may  save  to  the  owner  of  the  smoky  chim- 
ney, in  some  cases,  from  20  to  30  per  cent  of  his  coal  bill.  This 
means  2  per  cent  additional  dividends  to  the  stockholder  from 
this  saving  alone.  Thus,  we  see  that  the  question  of  smoke- 
less combustion  is  so  intimately  connected  with  that  of  furnace 
and  boiler  efficiency  that  the  prevention  of  smoke  is  a  sound 
economic  proposition. 

150.  Principles  of  Smokeless  Combustion. — To  obtain  perfect 
combustion  in  a  boiler  furnace,  the  furnace  itself  must  be  prop- 
erly designed  and  properly  operated.  Neither  of  these  features 
is  of  itself  sufficient  but  they  must  go  hand  in  hand.  The  fol- 
lowing general  statements  by  the  U.  S.  Geological  Survey 
indicate  the  lines  that  must  be  followed: 

1.  The  flame  and  the  distilled  gases  should  not  be  allowed 
to  come  in  contact  with  the  boiler  surfaces  until  combustion  is 
complete. 


THE  SMOKELESS  COMBUSTION  OF  COAL  '    181 

2.  Fire-brick  furnaces  of  sufficient   length  and  a  continuous 
or  nearly  continuous  supply  of  coal  and  air  to  the  fire  make  it 
possible  to  burn  most  coals  efficiently  and  without  smoke. 

3.  Coals    containing   a   large   percentage   of   tar    and   heavy 
hydrocarbons  are  difficult  to  burn  without  smoke,  and  require 
special  furnaces  and  more  than  ordinary  care  in  firing. 

4.  In  ordinary  boiler  furnaces   (hand  fired)   only  'coals  high 
in  fixed  carbon  can  be  burned  without  smoke,  except  by  expert 
firemen  using  more  than  ordinary  care  in  firing. 

5.  Combinations  of  boiler-room  equipment  suitable  for  nearly 
all  power  plant  conditions  can  be  selected,  and  can  be  operated 
without  objectionable  smoke  when  reasonable  care  is  exercised. 

6.  Of  the  existing  plants,  some  can  be  remodeled  to  advan- 
tage.    Others  cannot,  but  must  continue  to  burn  coals  high  in 
fixed   carbon   or  to   burn  other   coals   with   inefficient   results, 
accompanied  by  more  or  less  annoyance  from  smoke.     In  these 
cases,  a  new  and  well  designed  plant  is  the  only  solution  of  the 
difficulty. 

The  problem  of  smoke  prevention  is  very  intimately  con- 
nected with  that  of  securing  better  combustion  of  the  fuel, 
for  where  there  is  perfect  combustion  there  will  be  no  smoke. 
The  matter  of  the  actual  money  value  of  the  fuel  which  passes 
off  as  smoke  is  not  of  very  much  importance,  since  this  loss  is 
probably  never  more  than  2  per  cent  of  the  total  value,  but  the 
importance  of  smoke  prevention  lies  largely  in  the  suppression 
of  a  public  nuisance,  and  in  the  fact  that  the  presence  of  smoke 
usually  indicates  -incomplete  combustion  which  in  itself  is  a 
great  loss,  as  has  been  pointed  out  in  previous  chapters. 
The  whole  problem,  therefore,  resolves  itself  into  one  of 
securing  perfect  combustion  of  the  coal,  and  it  may  be  stated 
as  a  general  truth  that  "  any  fuel  may  be  burned  economically 
and  without  smoke  if  it  is  mixed  with  the  proper  amount  of  air 
at  a  proper  temperature." 

This  condition  may  be  secured,  according  to  Mr.  Wm.  Kent, 
by  fulfilling  the  four  following  conditions: 

(a)  Having  the  gases  distilled  from  the  coal  slowly. 

(b)  Bringing  the  gases,  when  distilled,  into  intimate  contact 
with  very  hot  air. 

(c)  Burning  the  gases  in  a  hot  fire-brick  chamber. 

(d)  Not  allowing  the  gases  to  come  into  contact  with  com- 
paratively cool  surfaces,  such  as  the  shell  or  tubes  of  a  steam 


182  STEAM  BOILERS 

boiler,  until  complete  combustion  has  taken  place;  this  means 
that  the  gases  shall  have  sufficient  space  and  time  in  which  to 
burn  before  they  are  allowed  to  come  into  contact  with  the 
boiler  surfaces. 

Smoke  consists  of  carbon  or  soot  in  a  light  flaky  form  which 
is  light  enough  to  float  in  air.  It  is  mixed  with  the  products 
of  combustion,  such  as  carbon  dioxide,  carbon  monoxide,  sul- 
phurous and  sulphuric  acid,  water,  nitrogen,  ammonia,  car- 
buretted  hydrogen,  and  other  vapors  of  lesser  note. 

151.  Causes  of  Smoke. — Before  taking  up  the  problem  of 
smoke  prevention  it  is  necessary  to  understand  fully  all  the  con- 
ditions which  contribute  to  smoke  making,  and,  therefore,  to 
the  proper  and  economical  combustion  of  the  fuel.  In  this  con- 
nection Professor  Olin  A.  Sandreth  of  Vanderbilt  University  in  a 
report  to  the  State  Board  of  Health  of  Tennessee  on  "  Smoke 
Prevention,"  says: 

"When  fresh  coal  is  thrown  on  a  bed  of  incandescent  coal,  or  is 
otherwise  highly  heated,  there  immediately  begins  the  distillation  of 
the  more  volatile  portions  of  the  hydrocarbons  in  the  coal,  which  distilled 
matter  is  burned  if  the  temperature  is  high  enough  and  a  sufficient 
supply  of  oxygen  is  present;  but  which  passes  up  the  chimney  as 
yellowish  fumes  if  either  of  these  two  essential  conditions  of  combustion 
is  wanting.  As  the  fresh  coal  becomes  more  highly  heated  the  less 
volatile  hydrocarbons  are  distilled,  and  these  being,  chemically  speaking 
unstable  compounds,  are  decomposed  or  dissociated  by  the  heat  at  a 
temperature  much  below  that  at  which  the  carbon  thus  liberated  com- 
bines with  oxygen  in  combustion.  The  temperature  necessary  for 
combustion  of  this  free  carbon  is  very  high,  approximately  2000°  F., 
and,  hence,  there  is  a  wide  margin  of  opportunity  for  this  portion  of  the, 
carbon  to  escape  unburned,  as  this  temperature  is  somewhat  difficult 
to  maintain  in  the  mass  of  gaseous  matter  above  the  coal." 

It  is  free  carbon,  unburned  and  in  a  finely  divided  state, 
which  produces  the  bright  luminous  flame,  and  which,  when 
cooled,  produces  the  black  clouds  of  smoke  that  issue  from  the 
chimney  and  which  afterward  settles  as  soot.  After  the  vola- 
tile matter  is  all  driven  off,  there  still  remains  the  fixed  car- 
bon, which  now  is  in  the  form  of  coke.  In  burning,  this  gives 
but  little  flame  and  no  smoke,  as  the  particles  are  not  detached 
from  the  solid  mass  until  combustion  takes  place. 

In  the  ordinary  boiler  furnace,  as  generally  constructed  and 
fired,  the  conditions  are  very  unfavorable  for  perfect  com- 
bustion during  the  period  in  which  the  volatile  matter  is  driven 


THE  SMOKELESS  COMBUSTION  OF  COAL       183 

off  from  each  charge  of  coal.  When  the  fixed  carbon  stage  is 
reached,  there  is  but  little  difficulty  in  maintaining  perfect 
combustion,  but,  when  a  fresh  charge  of  coal  is  added,  the 
difficulties  reappear;  the  air  supply,  if  not  in  excess  during 
the  burning  of  the  previous  incandescent  coal,  will  now  be  in- 
sufficient since  the  distillation  of  the  volatile  matter  calls  for 
an  increased  amount  of  air,  while,  in  fact,  the  greater  depth 
of  coal  now  on  the  grate  actually  reduces  the  supply. 

If  an  additional  supply  of  air  is  admitted  through  the  furnace 
doors,  it  will  be  cold  and  cannot  be  thoroughly  mixed  with  the 
combustible  gases.  Likewise,  the  furnace  temperature,  if  high 
enough  before  charging,  is  now  much  lower  owing  to  the  cooling 
effects:  first,  of  the  cold  air  rushing  in  when  the  doors  are 
opened;  second,  of  the  mass  of  coal;  third,  of  the  evaporation 
of  the  moisture  in  the  coal  and  of  the  distillation  of  the  volatile 
matter.  Thus,  we  see  that  at  the  time  a  high  temperature  is 
needed  to  burn  the  free  carbon,  the  furnace  is  coldest. 

In  fulfilling  the  requirements  of  sufficiency  of  supply  and 
thoroughness  of  mixing  the  air  with  the  combustible  gases, 
it  must  be  noted  that  these  conditions  should  not  be  secured  by  a 
reckless  surplus  of  air,  as  this  carries  away  useful  heat  which 
is  not  only  a  loss  in  itself,  but  may,  and  often  does,  result  in 
lowering  the  temperature  of  the  combustible  gases  below  their 
temperature  of  ignition,  thus  causing  the  escape  of  unburned 
fuel.  Owing  to  the  difficulty  of  effecting  such  a  thorough 
mixture  as  to  bring  to  each  combustible  particle  just  the  proper 
amount  of  air,  it  is  necessary  to  provide  a  surplus  of  air,  but 
this  should  be  considered  as  an  evil  to  be  kept  at  a  minimum 
by  the  most  thorough  mixing  possible. 

152.  Means  of  Prevention. — Passing  to  the  means  of  accom- 
plishing combustion  without  smoke  production,  it  is  safe  to 
say  that,  so  far  as  it  pertains  to  steam  boilers,  the  object  must 
be  attained  by  one  or  more  of  the  following  agencies : 

(1)  By  the  proper  design  and  setting  of  the  boiler  plant. 
This  implies  proper  grate  area,  sufficient  draft,  the  necessary 
air  admission  space  between  grate  bars  and  through   the  fur- 
nace, and  ample  combustion  room  under  boilers. 

(2)  By  that  system  of  firing  which  is  best  adapted  to  each 
particular  furnace  to  secure  the  perfect  combustion  of  bitumi- 
nous coal.     This  may  be  either  (a)  "coke  firing,"  or  charging 
all  coal  into  the  front  of  the  furnace  until  partially  coked,  and 


184  STEAM  BOILERS 

then  pushing  back  or  (b)  "alternate  firing"  or  (c)  " spreading" 
by  which  the  coal  is  spread  over  the  whole  grate  area  in  a  thin 
uniform  layer  at  each  charging. 

(3)  The   admission  of  air  through  the  furnace  door,  bridge 
wall,  or  side  walls. 

(4)  Steam  jets  or  other  artificial  means  of  thoroughly  mixing 
the  air  and  combustible  gases. 

(5)  Prevention  of  the  cooling  of  the  furnace  and  boilers  by 
the  inrush  of  cool  air  when  the  furnace  doors  are  opened  for 
charging  the  coal  and  handling  the  fire. 

(6)  Establishing  a  gradation  of  the  several  steps  of  combus- 
tion, so  that  the  coal  may  be  charged,  dried,  and  warmed  at  the 
coolest  part   of  the  furnace,    and  then   moved  by  successive 
steps  to  the  hottest  place,  where  the  final  combustion  of  the 
coked  coal  is  completed,  and  compelling  the  distilled  combustible 
gases  to  pass  through  the  hottest  part  of  the  fire. 

(7)  Preventing   the    cooling   by   radiation   of   the   unburned 
combustible  gases  until  perfect  mixing  and  combustion  has  been 
accomplished. 

(8) .  Varying  the  supply  of  air  to  suit  the  periodic  variation 
in  demand. 

(9)  The   substitution   of    a    continuous    uniform   feeding   of 
coal  instead  'of  the  intermittent  charges. 

(10)  Down  draft  burning,  or  causing  the  air  to  enter  above 
the  grates  and  pass  down  through  the  coal,  carrying  the  dis- 
tilled products   down  to   the   high   temperature   plane   at   the 
bottom  of  the  fire. 

(11)  Underfeeding,   or  causing  the  volatile   matter  and  air 
to  mix  and  pass  upward  through  the  incandescent  bed  of  coke, 
thus  causing  complete  combustion  of  the  volatile  matter. 

The  number  of  smoke  prevention  devices  are  legion.  Only 
a  brief  classification  of  the  principles  of  working  will  be  attempted 
here.  These  are: 

(a)  Mechanical  stokers,  which  automatically  deliver  the 
fuel  in  a  finely  divided  state  into  the  furnace  at  a  uniform  rate, 
and  which  also  keep  the  fire  clean  by  a  slow  but  constant  motion 
of  the  individual  sections  of  the  grate.  They  accomplish  their 
object  by  means  of  agencies  5,  6,  and  9,  and  sometimes  11, 
of  the  foregoing  list.  They  sometimes  effect  a  very  material 
saving  in  the  labor  of  firing,  and  are  efficient  smoke  preventers 
when  not  pushed  above  their  capacity,  and  when  the  coal  does 


THE  SMOKELESS  COMBUSTION  OF  COAL       185 

not  cake  badly.  They  are  rarely  susceptible  to  the  sudden 
changes  in  the  rate  of  firing  frequently  demanded  in  service. 
(6)  Air  flues  in  side  walls,  bridge  walls,  and  grate  bars,  through 
which  air  when  passing  is  heated  (agency  3).  The  results 
are  always  beneficial,  but  the  flues  are  difficult  to  keep  clean 
and  in  order. 

(c)  Coking  arches,   or  arched  over  spaces  in  front    of    the 
furnace  in  which  the  fresh  coal  is  coked,  both  to  prevent  cooling 
of  the  distilled  gases  and  to  force  them  to  pass  through  the 
hottest  part  of  the  furnace  just  beyond  the  arch  (agencies  6 
and  7).     The  results  are  good  for  normal  conditions,  but  in- 
effective when  the  fires  are  forced.     The  arches  are  also  easily 
burned  out  and  injured  by  working  the  fire,  and  are  expensive 
to  replace. 

(d)  Dead  plates,  or  a  portion  of  the  grate  next  to  the  furnace 
doors  reserved  for  warming  and  coking  the  coal  before  it  is 
spread  over  the   grate    (agency   6).     These   give   good  results 
when  the  furnace  is  not  forced  above  its  normal  capacity.     This 
embodies  the  coking  method  of  firing  mentioned  previously. 

(e)  Down   draft  furnaces,   or  furnaces   in  which   the   air  is 
supplied  above  the  coal  and  the  products  of  combustion  are 
carried  away  beneath  the  grate,  thus  causing  a  downward  draft 
through  the   coal,   carrying  the  distilled  gases  down  through 
the  highly  heated  incandescent  layer  of  coal  on  the  grate  (agency 
10).     In  this  furnace  the  grate  bars  must  be  kept  cool  by  the 
circulation  of  water  through  them,  as  they  have  to  bear  the 
hottest  portion  of  the  flame. 

(/)  Steam  jets  to  draw  or  inject  air  into  the  furnace  above 
the  grate,  and  also  to  mix  the  air  and  combustible  gases  (agency 
4).  A  very  efficient  smoke  preventer,  but  one  liable  to  be 
wasteful  of  fuel  by  inducing  too  rapid  a  draft. 

(g)  Baffle  plates  placed  in  the  furnace  above  the  fire,  to  aid 
in  mixing  the  combustible  gases  with  the  air  (agency  4) . 

(h)  Double  furnaces,  of  which  there  are  two  entirely  dif- 
ferent styles.  The  first  of  these  places  the  second  grate  below 
the  first.  The  coal  is  coked  on  the  first  grate,  during  which 
process  the  distilled  gases  are  made  to  pass  over  the  second 
grate,  where  they  are  ignited  and  burned;  the  coke  from  the 
first  grate  is  dropped  on  to  the  second  grate  and  burned  (agencies 
6  and  7).  This  is  a  very  efficient  and  economical  smoke  pre- 
venter, but  rather  complicated  to  construct  and  maintain.  In 


186 


STEAM  BOILERS 


the  second  form  the  products  of  combustion  from  the  first  fur- 
nace pass  through  the  grate  and  fire  of  the  second,  each  furnace 
being  charged  with  fresh  fuel  when  needed,  the  latter  gen- 
erally with  a  smokeless  coal  or  coke — an  irrational  and  unprom- 
ising method. 

It  is  no  longer  a  problem  whether  smoke  can  be  prevented  or 
not.     This  has  been  settled  conclusively  in  the  affirmative  in 


FIG.  87. 


a  number  of  localities  where  proper  laws  for  the  abatement  of 
smoke  have  been  passed  and  enforced.  It  must  be  borne  in 
mind  that  the  method  which  is  successful  in  preventing  smoke 
with  one  kind  of  coal  may  not  be  successful  with  another  kind, 
and  each  particular  kind  of  coal  will  have  to  receive  its  own 
consideration  in  the  design  of  a  furnace  for  smokeless  combus- 


THE  SMOKELESS  COMBUSTION  J)F  COAL       187 

tion.  The  principles  laid  down  above  are,  however,  of  a  general 
nature  and  apply  to  all  ordinary  grades  of  smoke-producing 
coals. 

An  extensive  series  of  experiments  have  recently  been  con- 
ducted by  the  Engineering  Experiment  Station  of  Illinois  with 
a  view  to  devising  methods  of  burning  Illinois  coals  without 
smoke.  From  these  experiments  it  has  been  determined  that 
the  method  of  setting  the  boiler  and  furnace  exerts  considerable 
influence  upon  smoke  production.  A  number  of  different  kinds 
of  settings  were  built  and  tried.  Some  of  those  which  proved 


FIG.  88. 

successful  in  preventing  smoke  are  shown  in  Figs.  87,  88,  and  89. 
The  dimensions  shown  on  all  these  drawings  are  general  dimen- 
sions which  will  serve  as  a  guide  in  proportioning  the  setting  for 
other  sizes  of  boilers. 

In  all  of  these  settings,  it  will  be  noticed  that  one  feature  is 
common — the  gases  travel  for  a  considerable  distance  before 
coming  in  contact  with  any  surfaces  by  which  they  would  be 
cooled  to  any  considerable  degree.  This  gives  the  volatile  gases 
a  chance  to  be  burned  completely  before  they  come  in  contact 
with  the  cold  metal  surfaces  and  to  be  cooled  to  such  a  tempera- 
ture that  chemical  combination  with  oxygen  would  be  impossible. 
It  will  be  remembered  that  a  high  temperature  is  required  for  each 
atom  of  carbon  to  unite  with  two  atoms  of  oxygen  to  form  carbon 


188 


STEAM  BOILERS 


dioxide.  Therefore  it  is  of  extreme  importance  that  the  hot 
gases  should  not  come  in  contact  with  any  surface  which  will 
cool  them  before  combustion  is  completed.  In  the  settings  of 
horizontal  water-tube  boilers,  just  shown,  it  will  be  noticed  that 
the  tubes  have  been  covered  with  tile  to  prevent  the  hot  gases 
from  coming  in  contact  with  them  and  being  cooled  before 
combustion  has  been  completed.  For  this  purpose,  the  hot 
gases  should  be  made  to  travel  from  6  to  8  ft.  before  coming  in 
contact  with  any  cooling  surfaces. 


11  Tubes  High 

10  Tubes  Wide,  5  Rows 

11  Tubes  Wide.  6  Hows 


FIG.  89. 


153.  Types  of  Furnaces. — Mechanical  stokers,  when  properly 
set  and  operated,  produce  better  results  than  hand  firing,  but 
any  stoker  is  effective  only  when  set  so  that  the,  principles 
of  combustion  are  properly  observed.  Although  hand-fired 
furnaces  may  be  operated  without  objectionable  smoke,  the 
fireman  is  so  variable  a  factor  that  the  best  solution  depends  on 
the  mechanical  stoker.  It  is  not  possible  to  say  that  any  one 
type  of  stoker  is  the  best,  since  no  type  is  equally  valuable  for 
burning  all  kinds  of  coal.  If  the  furnace  is  in  every  case  properly 
designed  for  the  stoker  that  is  used,  there  will  be  found  little 
difference  in  the  efficiencies  of  the  different  types.  The  primary 
requisite  is  to  set  the  stoker  so  that  combustion  may  be  completed 
before  the  gases  strike  the  heating  surface  of  the  boiler.  When 
partly  burned  gases  strike  the  comparatively  cold  surfaces  of  a 


THE  SMOKELESS  COMBUSTION  OF  COAL       189 

boiler,  combustion  is  necessarily  hindered  or  completely  pre- 
vented, and  smoke,  together  with  a  reduced  efficiency,  results. 

The  length  of  time  required  for  gases  to  travel  from  the  grates 
to  the  heating  surface  probably  averages  less  than  one  second, 
which  shows  that  the  gases  and  air  must  be  intimately  mixed 
as  soon  as  the  gases  are  distilled,  otherwise  the  gases  may  pass 
out  of  the  furnace  and  become  cooled  before  having  come  in 
contact  with  sufficient  oxygen  to  burn  them.  This  shows-  the 
desirability  of  some  device  for  mixing  the  green  gases  with  the 
necessary  air  for  combustion  as  they  are  distilled. 

The  remaining  articles  in  this  chapter  give  the  conclusions  of 
the  Geological  Survey  as  to  the  use  of  different  types  of  stokers 
and  the  proper  settings  for  them. 

154.  Chain  Grates. — The  majority  of  stokers  of  this  type  are 
particularly   adapted  to  free   burning   coals,   high   in   volatile 
matter,  such  as  are  mined  in  the  central  and  western  fields.     As 
they  burn  the  cheapest  grades  of  non-caking  coals  with  complete 
combustion  they  offer  a  valuable  means  of  producing  power 
cheaply.     Small  sizes  of  coal  seem  to  be  preferred.     The  chief 
difference  in  different  makes  is  in  the  length  of  the   fire-brick 
arch  which  extends  over  the  whole  width  of  the  grate  and  extends 
from  the  hopper  backward.     The  tendency  is  to  lengthen  this 
arch  and  to  proportion  its  length  and  slope  to  the  coals  used. 
This  arch  is  a  highly  desirable  feature  as  it  prevents  the  gases 
from  being  cooled  and  aids  considerably  in  mixing  the  gases  and 
air  while  maintaining  the  high  temperature  necessary  for  com- 
bustion.    With  many  water-tube  boilers  the  arch  is  made  short, 
this  construction  being  especially  common  in  the  Middle  West. 
This  short  arch,  and  the  consequent  brief  travel  to  the  heating 
surface  from  the  grates,  are  features  which  are  unfavorable  to 
smokeless  combustion.     These  grates  are  liable  to  form  dense 
smoke  under  variable  loads  unless  properly  handled.     A  sudden 
release  of  load  requires  a  reduction  of  draft  which  is  often  carried 
too  far.     The  draft  should  never  be  closed  beyond  a  certain 
position  which  can  be  determined  by  experiment.     For  changes 
of  load  it  is  far  better  to  change  the  depth  of  the  fire  than  the 
rate  of  travel  of  the  grate. 

155.  Inclined  Grate  with  Front  Feed. — Smokeless  operation 
can  be  obtained  with  these  grates  by  careful  operation  and  the 
use  of  steam  jets  or  the  generous  admission  of  air,  but  as  a  rule 
they  are  set  too  close  to  the  heating  surface  and  the  coking  arch 


190  STEAM  BOILERS 

is  made  too  short.  These  stokers  can  force  a  fire  quickly  but 
tests  show  that,  as  usually  set,  more  than  average  attention  is 
required  to  prevent  smoke.  The  coking  arch  should  be  extended 
beyond  that  generally  used  and  if,  with  water-tube  boilers,  the 
bottom  row  of  tubes  is  tiled  so  as  to  give  a  long  passage  to  the 
gases  before  reaching  the  heating  surface,  much  better  results 
may  be  expected. 

156.  Side-feed  Stokers. — These  stokers,  or  furnaces,  are  char- 
acterized by  large  coking  spaces  and  ample  combustion  chambers. 
As  constructed  at  present,  they  all  have  a  fire-brick  arch  extending 
over  the  entire  grate  area  and  have  openings  for  admitting  hot 
air  just  above  the  coal  at  the  point  where  the  volatile  matters 
are  distilled.     These  features  help  to  ensure  smokeless   com- 
bustion.    The  Survey  report  states  that  no  other  type  of  stoker 
was  found  doing  so  well  under  so  great  a  variety  of  conditions. 
The  chief  trouble  was  found  in  the  device  for  discharging  the 
ash.     It  was  found  that  these  stokers  smoked  in  some  of  the 
earlier  installations  which   did   not   have  the   arch   extending 
over  the  whole  grate  area. 

157.  Underfeed  Stokers. — These  stokers  maintain  the  fire  in  a 
long  heap  in  the  middle  of  the  furnace  and  feed  the  fresh  coal 
underneath  the  burning  mass  so  that  the  volatile  gases  must 
pass  upward  through  it.     The   clinker  formed  from  the   ash 
collects  at  the  sides  and  is  removed  through  the  front  of  the 
furnace.     These  stokers  are  nearly  always  used  with  mechanical 
draft,  and  the  latest  models  are  installed  with  automatic  con- 
trol for  both  air  and  fuel,  so  that  the  relative  amounts  of  air  and 
coal  maybe  adjusted,  and  these  will  then  continue  automatically. 
This  stoker  requires  no  fire-brick  arch  and  the  combustion  space 
required  is  less  than  for  any  other  type,  although  even  here  the 
gases  should  not  be  allowed  to  strike  the  heating  surface  too 
soon.     From  these  facts  we  see  that  this  type  is  well  suited  to 
replace  hand  firing  in  an  old  plant  where  the  space  is  limited 
and  where  the  old  settings  cannot  be  altered  materially.     It  is 
also   notable  for  the  ease   and  economy  of   carrying  variable 
loads.     This  stoker  has  been  successfully  applied  to  internally 
fired  boilers  of  the  locomotive  and  marine  types.     The  only 
variable  element  in  operation  is  the  cleaning  of  the  fires  and, 
if  the  fireman  is  careful  to  burn  the  fires  well  down  before  cleaning 
or  breaking  up,  there  will  be  no  difficulty  about  smoke.    M  n 

158.  Hand-fired  Furnaces. — With  hand  firing  the  best  results 


THE  SMOKELESS  COMBUSTION  OF  COAL       191 

are  obtained  when  the  firing  is  done  frequently  and  in  small 
charges.  The  greatest  trouble  from  smoking  is  during  and  just 
after  charging,  but,  if  air  is  admitted  freely  during  these  times 
so  as  to  oxidize  the  volatile  matter,  the  smoke  will  be  reduced. 

Tests  seem  to  show  a  higher  economy  and  less  smoke  with 
rocking  grates  than  with  stationary  grates  where  coals  that  do  not 
clinker  excessively  are  used.  All  hand-fired  furnaces  which  will 
burn  coal  without  objectionable  smoke,  approach  the  theory  of 
the  mechanical  stoker,  but  owing  to  the  variable  personal  element 
they  cannot,  under  average  conditions,  give  as  good  results. 
In  most  successful  hand-fired,  furnaces  the  travel  of  the  gases 
from  the  grates  to  the  heating  surface  is  lengthened,  and  many 
types  use  the  fire-brick  arch  or  the  Dutch  oven.  The  design 
of  some  furnaces  shows  recognition  of  the  value  of  thoroughly 
mixing  the  air  and  gases;  and  arches,  retorts,  piers,  or  steam  jets 
are  used  for  this  purpose. 

When  steam  jets  are  used,  they  should  be  arranged  to  be 
automatically  thrown  into  use  when  the  door  is  opened  for 
firing  and  should  remain  in  operation  for  a  short  time  following 
the  closing  of  the  door.  The  steam  jet  is  found  usually  in  a 
furnace  that  is  improperly  designed  or  that  has  too  small  an 
air  supply.  It  is  an  uneconomical  device,  but  doubtless  often 
aids  in  preventing  smoke  by  compelling  the  air  and  gases  to  mix 
thoroughly.  The  claim  sometimes  made  that  the  use  of  a  steam 
jet  will  increase  the  thermal  value  of  the  fuel  is  erroneous  as  a 
steam  jet  which  is  operated  continuously  is  a  source  of  consider- 
able loss. 

Cracking  the  furnace  door  for  a  period  following  stoking 
aids  considerably  in  efficiency  and  smokelessness,  but  introduces 
the  personal  element.  Automatic  air  openings  in  the  doors  are 
also  used.  The  coking  furnace  requires  less  care  on  the  part  of 
the  fireman  to  secure  smokeless  combustion  but  unless  care  is 
taken  excess  air  is  liable  to  leak  through  and  reduce  the  efficiency. 

The  down  draft  furnace  as  ordinarily  used  has  an  upper 
grate  formed  of  water  tubes  through  which  water  circulates. 
Coal  is  fed  upon  this  grate  and,  after  being  partially  burned,  falls 
upon  the  lower  grate,  where  combustion  is  completed  by  the 
excess  of  air  drawn  through  the  upper  and  lower  grates.  The 
distilled  gases  from  the  fresh  fuel  pass  through  the  fuel  bed  on 
the  upper  grate,  thus  being  thoroughly  mixed  with  air  and 
facilitating  combustion  between  the  grates.  Fig.  90  illustrates 


192 


STEAM  BOILERS 


the  application  of  this  form  of  furnace  to  a  return  fire-tube 
boiler,  and  shows  the  method  of  connecting  the  grates  to  the 
water  space  and  the  boiler. 

There  are  many  small  hand-fired  power  plant  units  which 
smoke  badly.  The  construction  of  many  of  these  furnaces  is 
such  that  it  is  almost  impossible  to  operate  the  plant  without 
smoke.  Still,  something  might  be  done  to  reduce  the  smoke 
if  the  firemen  exercised  more  care  in  firing.  Whatever  can 
be  done  by  firemen  in  the  way  of  properly  introducing  the 
fuel  into  the  furnace  is  just  so  much  gained,  and  it  relieves  the 
auxiliary  mixing  devices  or  baffles,  if  such  exist,  from  just  so 
much  work  later  on. 


FIG.  90. — Hawley  down-draft  furnace. 

The  best  method  of  hand  firing  for  smokelessness  is  also  the 
best  method  for  economy.  The  spreading  method  is  satisfactory, 
and  generally  used  for  anthracite;  the  coking  method  for  caking 
coals  and  the  alternate  for  non-caking  coals.  It  is  the  alternate 
method  which  is  best  suited  to  most  of  the  coals  used  in  dis- 
tricts of  Wisconsin,  Michigan,  and  Illinois.  This  method  allows 
much  of  the  air  supply  to  come  through  the  bright  fuel  bed,'  and 
thus  become  heated  and  suitable  for  mixing  with  the  highly 
volatile  content  which  is  being  rapidly  driven  from  the  freshly 
fired  coal  on  the  other  side.  Just  because  fresh  fuel  has  been 
spread  over  one  part  of  the  fuel  bed,  the  air  most  needed  at  that 
moment  cannot  as  easily  flow  through  it,  and  another  part  of  the 
fuel  bed  should  be  left  free  for  its  passage  at  that  time. 

When   the  fuel   bed  area  is  very  large,  some  checker   board 


THE  SMOKELESS  COMBUSTION  OF  COAL       193 

system  of  firing  in  which  the  coal  is  fired  in  small  thin  patches 
may  be  adopted.  When  alternately  fired  and  left  free  for  air 
passage,  this  will  result  in  a  large  reduction  in  the  amount  of 
smoke  produced  by  the  too  common  method  of  spreading  the 
coal  over  the  entire  surface  at  each  firing. 

It  must  not  be  forgotten  that  a  large  supply  of  warm  air  is 
needed  immediately  after  fresh  fuel  is  spread  over  a  part  or 
all  of  the  fuel  bed;  this  is  best  supplied  as  just  explained,  but  it 
may  be  advantageous  to  provide  for  still  more  air  by  leaving 
the  fire  doors  open  slightly  just  after  each  firing. 


FIG.  91. — Climax  smoke  preventer. 

There  are  several  devices  on  the  market  which  provide 
for  an  air  supply  over  the  fire,  which  are  turned  on  with  the 
opening  or  closing  of  the  fire  door  and  which  can  be  arranged  to 
close  at  the  end  of  any  desired  time  depending  upon  the  rate  of 
driving  and  frequency  of  firing  found  desirable.  Fig.  91  illus- 
trates the  application  of  the  Climax  Smoke  Preventer  which 
is  a  device  for  accomplishing  this  purpose.  This  device  blows 
steam  into  the  furnace  above  the  fire  through  a  nozzle  whose 
mouth  is  between  1/16  and  1/8  in.  in  diameter.  The  nozzle  is 
surrounded  by  a  piece  of  pipe  of  larger  diameter  through  which 
air  is  drawn  by  the  jet  of  steam.  The  jet  of  steam  is  directed 
toward  the  bridge  wall  for  the  purpose  of  thoroughly  mixing 
the  air  with  the  volatile  gases  being  distilled  from  the  coal.  The 
steam  jet  is  started  when  the  furnace  door  is  opened  and  is 
closed  at  a  definite  time  after  the  door  is  opened,  by  an  electro- 

17 


194  STEAM  BOILERS 

magnet  operated  from  a  clock  mechanism.  The  time  at  which 
closing  occurs  may  be  easily  changed  by  the  fireman  to  suit 
the  frequency  of  firing  and  the  quality  of  coal  that  is  being 
used.  If  desirable,  several  of  these  steam  jets  may  be  attached 
to  a  single  furnace. 

The  firing  of  small  amounts  of  coal  at  frequent  intervals  pro- 
duces less  smoke  than  the  firing  of  large  amounts  at  long  intervals. 
The  latter  method,  however,  usually  proves  less  tiresome  to  the 
fireman  and  is  for  that  reason  more  frequently  adopted  by  him 
unless  he  is  closely  supervised. 

While  careful  hand  firing  will  reduce  the  smoke  considerably, 
the  chief  difficulty  is  that  nearly  all  hand-fired  furnaces  are 
improperly  designed.  The  customary  setting  for  a  hand-fired 
fire-tube  boiler  is  all  wrong  except  for  anthracite  coal  or  coke. 
Placing  the  grate  directly  beneath  the  boiler  shell  is  in  direct 
violation  of  principles  c  and  d  given  on  page  185.  The  bridge 
wall  further  deflects  the  gases  against  the  shell  as  they  pass 
over  it.  No  matter  what  care  is  taken  in  firing,  the  hydro- 
carbons cannot  be  completely  burned  under  such  conditions.  To 
remedy  this,  the  grate  should  be  moved  forward  at  least  a  dis- 
tance equal  to  its  own  length,  so  it  will  be  entirely  out  from  under 
the  boiler,  and  an  arched  fire-brick  furnace  built  over  it.  This 
furnace  should  be  high  and  roomy,  so  that  the  gases  from  the  coal 
will  not  be  drawn  out  too  quickly.  Another  important  point  is  to 
have  the  gases  thoroughly  mixed  before  they  become  cooled.  In 
this  way,  the  surplus  oxygen  that  may  be  admitted  at  one  point 
will  be  available  for  burning  the  excess  of  hydrocarbons  that  is 
driven  off  at  another  point  of  the  fire.  This  may  be  done  by 
steam  jets  or  by  baffle  plates.  In  some  cases,  the  shape  of  the 
furnace  and  bridge  wall  has  been  found  to  create  eddy  currents 
sufficient  to  mix  the  gases  thoroughly  in  the  furnace. 

It  will  be  seen  that  the  chief  difficulty  of  hand-fired  furnaces 
is  the  irregular  supply  of  coal  and  the  consequent  variation  in 
the  proportions  of  the  air  and  fuel.  Nearly  all  devices  aiming 
to  make  hand-fired  furnaces  smokeless  are  merely  devices  in- 
tended to  increase  more  or  less  automatically  the  air  supply  when 
more  air  is  needed.  The  best  solution  of  this  part  of  the  problem, 
however,  is  the  use  of  a  mechanical  stoker  which  will  deliver 
a  continuous  supply  of  fuel.  Then  if  the  stoker  is  properly  set 
and  operated,  even  the  peats  and  lignites  can  be  burned  with 
little  or  no  smoke. 


CHAPTER  XIII 
SETTINGS 

159.  Foundations. — In   selecting  the  location  of  boilers,   at- 
tention should  be  given  to  the  nature  of  the  soil  upon  which 
they  are  to  rest.     It  is  always  better  to  construct  a  foundation 
for  the  walls  of  the  setting  to  rest  upon,  as  this  will  insure  their 
permanent  alignment.     If  the  soil  is  firm,  the  foundation  may 
be  light,  but  if  the  soil  is  not  firm,  the  foundation  should  be 
heavier  and  more  extensive.     The  foundation  is  usually  con- 
structed of  concrete,  but  stone  or  even  brick  may  also  be  used 
where  more  convenient. 

160.  Setting  for  Fire-tube   Boilers. — The  setting  for  a  boiler 
includes  the  general  arrangement  of  furnace,  boiler,  and  chimney, 
in  relation  to  one  another  and  the  manner  in  which  the  furnace 
and  boiler  are  enclosed  and  built  in.     For  the  ordinary  return 
fire-tube  boiler,  which  is  the  most  common  type,  there  are  two 
standard  forms  of  setting,  known  as  the  full-arch  front  and  the 
half -arch  front.     The  full-arch  front  is  also  known  as  a  flush  front 
because  the  front  of  the  setting  is  flush  with  the  smoke  box 
which  is  formed  within  the  setting.     The  front  of  this  setting 
is  in  the  form  of  a  large  rectangular  cast-iron  plate  with  open- 
ings for  the  firing,  ash  pit   doors,  and  flue  doors.     The  front 
is  of  more  or  less  ornamental  design  and,  when  boilers  are  set 
in  a  battery,  gives  a  very  neat  appearance.     A  flush  front  setting 
is  shown  in  Fig.  5.     The  smoke  connection  in  this  setting  is  cut 
off  from  the  furnace  by  a  sheet  of  steel  bent  into  a  half  circle,  as 
shown  in  Fig.  4.     This  half  circle  is  bolted  on  one  side  to  the 
shell  of  the  boiler  and  the  other  side  fits  up  close  to  the  front. 

The  half-arch  front  is  sometimes  known  as  the  overhung  front, 
from  the  fact  that  the  smoke  box,  or  front  connection,  extends 
out  in  front  of  the  setting  instead  of  being  formed  inside.  The 
cast-iron  front,  instead  of  being  rectangular,  extends  up  to  the 
boiler  and  fits  up  underneath  the  curve  of  the  shell.  The  boiler 
shown  in  Fig.  92  has  an  overhung  front.  From  this  illustration 
it  can  be  seen  that  the  front  is  in  two  parts;  the  lower  one  extends 
up  to  about  the  middle  of  the  boiler  while  the  upper  part  fits 

18  195 


196 


STEAM  BOILERS 


around  the  top,  giving  a  neat  appearance  to  the  front.  Fig.  92 
also  illustrates  the  method  of  fastening  the  cast-iron  front  to  the 
brickwork  by  means  of  long  bolts,  which  pass  entirely  through 
the  setting  from  front  to  rear,  the  bolts  being  imbedded  in  the 
brickwork.  The  overhung  front  is  somewhat  less  expensive 
than  the  flush  front,  but  it  has  the  disadvantage  that  the  end 
of  the  boiler  projects  out  past  the  front  and  makes  the  operation 
of  throwing  coal  into  the  furnace  a  little  more  difficult. 

The  smoke  connection  to  a  boiler  with  an  overhung  front 
is  made  to  the  projecting  end  of  the  boiler,  the  bottom  part  of 
the  smoke  box  being  enclosed  by  a  steel  band  as  in  the  flush  front. 
If  the  boiler  is  small  and  a  light  steel  stack  is  used,  the  weight 
of  the  stack  may  rest  directly  on  the  boiler.  Heavier  stacks 


SIDE   ELEVATION  FRONT  ELEVATION 

FIG.  92. — Setting  of  fire-tube  boiler  with  overhung  front. 

should  be  built  independent  of  the  boiler,  and  connection  made 
by  a  breeching  passing  from  the  smoke  connection  to  an 
opening  in  the  side  of  the  stack. 

When  two  or  more  boilers  are  set  side  by  side  with  common 
front  and  rear  walls,  they  form  what  is  termed  a  battery  of  boilers. 
All  the  boilers  of  a  battery  may  or  may  not  be  connected  to  the 
same  chimney. 

A  standard  setting  for  return  fire-tube  boilers,  recommended 
by  the  Hartford  Steam  Boiler  Inspection  and  Insurance  Company, 
is  shown  in  Fig.  93.  In  this  setting  the  furnace  is  lined  with 
fire  brick  and  the  walls  are  made  very  thick.  In  the  cross-hatch- 
ing on  the  illustration,  the  alternate  full  and  dashed  lines  represent 
fire  brick.  The  full  lines  represent  common  brick.  In  describ- 
ing this  setting  the  company  has  the  following  to  say: 

"The  width  of  the  furnace  in  the  settings  advocated  by  this  company 
is  6  in.  less  than  the  diameter  of  the  boiler.  Beginning  just  above  the 


SETTINGS 


197 


198  STEAM  BOILERS 

grate,  the  side  walls  batter  at  such  an  angle  as  to  make  them  3  in.  clear 
of  the  boiler  at  its  center,  where  the  walls  project  toward  and  close 
against  the  boiler.  The  batter  gives  greater  stability  to  the  walls,  and 
another  special  feature  of  it  is  that  it  allows  the  heated  gases  to  rise 
without  impinging  against  the  walls  of  the  setting,  and  they  flow  away 
from  the  walls  and  distribute  themselves  evenly  over  the  whole  heating 
surface  of  the  shell.  The  removal  of  ash  and  soot  is  also  facilitated  and, 
moreover,  it  is  found  that  these  deposits  do  not  form  so  readily  when  the 
walls  are  battered  as  they  do  when  the  walls  are  straight  and  the  space 
between  them  is  correspondingly  contracted.  The  batter  also  increases 
the  volume  of  the  combustion  chamber  and  allows  of  a  more  thorough 
mixing  of  the  oxygen  and  furnace  gases,  the  result  being  that  complete 
combustion  of  the  fuel  is  greatly  facilitated.  The  bridge  walls  slope 
back  from  about  4  in.  above  the  grate  at  an  angle  of  40  degrees  in 
order  that  the  radiant  heat  from  the  fire  may  be  diffused  over  a  large 
portion  of  the  boiler  shell. 

"  The  flame  bed  back  of  the  bridge  wall  slopes  down  to  the  level  of  the 
boiler  room  floor.  It  is  paved  for  easy  cleaning,  and  the  combustion 
chamber  is  large  enough  to  make  examination  and  repairs  to  the  boiler 
comparatively  easy.  The  cleaning  door  in  the  rear  wall  is  placed  on  a 
level  with  the  flame  bed,  in  order  that  ashes  may  be  readily  removed, 
and,  as  it  is  below  the  currents  of  highly  heated  gases,  loss  by  radiation 
through  the  door  is  largely  prevented.  The  loss  or  waste  of  heat  through 
this  cause  is  often  very  great  and  it  has  not  generally  received  the 
attention  it  deserves. 

"Another  point  that  demands  more  attention  than  it  usually  receives 
is  the  liability  of  leakage  of  cold  air  through  the  walls  of  the  setting, 
with  the  resulting  reduction  of  furnace  temperature.  To  avoid  loss  of 
temperature  from  this  cause,  heavy  double  walls  are  constructed  in  this 
company's  settings,  the  outside  walls  of  a  battery  having  a  2-in.  air 
space  between  them.  The  division  walls  between  two  or  more  boilers 
should  have  a  half-inch  clear  space  between  them,  to  allow  free  and 
independent  expansion  of  the  walls.  With  a  solid  wall  and  one  or  more 
boilers  of  the  battery  stopped,  one  side  of  the  waif  separating  a  boiler 
in  use  from  one  out  of  use  would  be  hot  and  greatly  expanded,  while 
the  other  side  of  it  would  be  cool;  the  result  being  that  the  bonded  or 
solid  wall  must  necessarily  be  strained  or  injured,  and  the  joints  in  the 
masonry  quite  probably  broken  by  the  unequal  expansion.  Excessive 
leakage  of  air  is  likely  to  follow.  These  criticisms  apply  to  all  solidly 
built  boiler  settings.  While  the  heavy  double  walls  are  somewhat 
more  expensive  in  first  cost,  the  increased  economy  and  capacity  of  the 
boilers  as  well  as  the  greater  durability  of  the  settings,  fully  warrant 
their  construction.  The  results  obtained  in  many  large  plants  fully 
sustain  this  statement. 


SETTINGS  199 

"  The  exposed  portion  of  the  boiler  shells  above  the  settings  are  cov- 
ered with  plastic  non-conducting  covering  2^  in.  thick.  This  is  much 
lighter  than  brick,  it  is  a  better  non-conductor,  and  does  not  exert  a 
sensible  thrust  upon  the  setting  walls  as  a  brick  arch  does.  If  leaks 
occur  along  the  joints  of  the  covered  part  of  the  boiler,  they  are  quickly 
noted  by  the  discoloration  of  the  covering,  and  may  be  stopped  before 
injury  from  corrosion  occurs. 

"The  illustrations  give  the  general  arrangement  of  the  settings 
described  above,  in  which  it'  is  desired  to  combine  durability  with 
simplicity  in  design  and  construction,  and  at  the  same  time  to  obtain 
good  results  from  the  boilers,  both  in  economy  and  capacity." 

For  estimating  the  number  of  bricks  required  to  set  return 
fire-tube  boilers  according  to  the  plans  just  described,  the 
table  on  the  next  page  will  be  useful. 

Good  hard  burned  brick  should  be  used,  set  in  strong  mortar 
of  cement  or  lime  and  cement.  The  brickwork  should  not  touch 
the  boiler,  as  bricks  absorb  moisture  and  retain  it  a  long  time, 
thus  rendering  the  boiler  liable  to  corrosion  at  a  place  not  easily 
seen.  A  better  plan  is  to  fill  all  spaces  between  the  boiler  and 
masonry  with  fire  clay. 

However  set,  all  boilers  must  be  allowed  ample  freedom  for 
expansion  and  contraction,  to  prevent  the  setting  from  being 
damaged.  The  brickwork  is  often  laid  so  close  to  the  boiler 
that  the  rivet  heads  are  imbedded  in  the  masonry  and,  when 
expansion  occurs,  the  walls  are  damaged  at  a  place  not  easily 
seen.  To  prevent  this,  an  iron  angle  is  sometimes  riveted  along 
the  sides  of  the  shell  and  the  brickwork  brought  up  to  it  instead 
of  up  to  the  shell  itself. 

In  building  brick  settings,  if  any  trimming  of  bricks  has  to  be 
done,  red  brick  should  be  trimmed  in  preference  to  the  fire 
brick  as  the  broken  section  of  a  fire  brick  is  quickly  attacked  by 
heat,  causing  it  to  crumble.  For  the  same  reason,  no  pieces  of 
fire  brick  should  be  used  unless  the  unbroken  side  can  be  turned 
toward  the  fire.  The  fire-brick  lining  should  be  independent  of 
the  balance  of  the  setting,  as  it  will  require  repairing  from  time  to 
time  and  it  is  desirable  that  the  lining  may  be  taken  down  and 
replaced  without  disturbing  the  balance  of  the  setting. 

The  tops  of  many  externally  fired  boilers  are  covered  with  a 
brick  arch  resting  on  the  side  walls.  This  is  not  a  good  plan  as 
leaks  are  liable  to  occur  and  not  be  noticed.  A  better  plan  is  to 
build  the  side  walls  up  a  little  higher  than  the  top  of  the  boiler, 


200 


STEAM  BOILERS 


MATERIAL  REQUIRED  FOR  BOILER  SETTINGS 
FULL  FLUSH  AND  OVERHANGING  FRONT  SETTINGS 


Diam- 
eter of 
boiler 
inches 

30 

Length 
of 
boiler 
feet 

Number  of 
fire  brick 
for 
one  boiler 

Pounds  of 
fire  clay 

Number  of  common  brick 

For  one 
boiler 

For  two 
boilers 

For  each 
additional 
boiler 

Full 
flush 

Over- 
hang 

Full 
flush 

Over- 
hang 

Full 
flush 

Over- 
hang 

Full 
flush 

Over- 
hang 

Full 
flush 

Over- 
hang 

8 
10 

686 

779 

275 
315 

4286 
4974 

6493 
7473 

2207 
2499 

36 

8 
10 
12 

772 
883 
980 

310 
355 
390 

4863 
5551 
6197 

•• 

7385 
8372 
9296 

2522 
2821 
3099 

42 

10 
12 
14 

1045 
1173 
1281 

420 

470 
515 

6212 
6902 
7666 

9400 
10383 
11477 

3189 
3481 
3811 

44 

10 
12 
14 

1066 
1183 
1310 

430 
475 
525 

6258 
6992 
7756 

9860 
10960 
12107 

3602 
3969 
4351 

48 

12 
14 
16 

1509 
1662 
1811 

1318 
1480 
1627 

605 
670 
725 

530 
590 
650 

12312 
13618 
14832 

11475 
12691 
13995 

18730 
20620 
22374 

17505 
19260 
21150 

6417 
7002 
7542 

6030 
6570 
7155 

54 
60 

14 
16 

1843 
1990 

1627 
1786 

740 
795 

650 
'  715 

14477 
15781 

13478 
14658 

21980 
23867 

20520 
22316 

7501 
8086 

7043 
7658 

14 
16 

18 

2109 

2278 
2458 

1831 
2002 
2180 

845 
915 
985 

735 
800 

875 

16208 
17588 
19058 

15038 
16418 
17888 

24720 
26716 

28786 

23010 
25006 
27136 

8513 
9128 
9728 

7973 
8588 
9248 

66 

72 

16 

18 

2495 
2677 

2186 
2364 

998 
1070 

875 
945 

18838 
20308 

17408 
19044 

28765 
30745 

26716 
29042 

9927 
10437 

9308 
9998 

16 
18 
20 

2770 
2971 
3163 

2424 
2611 
2816 

1110 
1190 
1265 

970 
1045 
1130 

20693 
22513 
24059 

19185 
20895 
22641 

31666 
34306 
36549 

29460 
32035 
34470 

10973 
11793 
12490 

10275 
11140 
11830 

78 

18 
20 

3250 
3499 

2861 
3110 

1300 
1400 

1145 
1245 

23688 
25769 

21988 
24254 

36025 
39242 

33530 
37022 

12377 
13473 

11543 
12768 

84 

18 
20 

3603 
3831 

3162 
3372 

1445 
1535 

1265 
1350 

29811 
32015 

27740 
29960 

46160 
49453 

43055 
46363 

16350 
17438 

15315 
16403 

Notes. — When  boilers  are  set  on  brackets,  the  piers  of  foundation  are  omitted. 

Fire  brick  figured  to  line  the  entire  surface  of  furnace,  including  floor  of  combustion  cham- 
ber, every  fifth  course  to  be  a  header  course. 

Fire  clay,  figured  on  basis  of  400  Ib.  of  fire  clay  per  thousand  of  fire  brick. 

Common  brick — one  barrel  of  Portland  cement,  one  barrel  of  lime  and  5/8  cu.  yd.  of  sand 
will  lay  1000  common  brick. 


SETTINGS  201 

and  fill  in  over  the  top  with  clean  dry  sand,  which  can  easily  be 
brushed  aside.  A  still  better  plan  is  the  use  of  a  non-conducting 
covering  as  described  before. 

161.  Boiler  Supports. — Fire-tube  boilers  are  usually  supported 
either  by  brackets  riveted  to  the  shell  and  resting  on  the  side 
walls,  or  suspended  by  straps  riveted  to  the  shell.  A  well  designed 
support  should  allow  free  expansion  of  the  boiler  and  distribute 
the  weight  equally  among  the  different  supports. 

Boiler  brackets  are  made  of  cast  iron  or  stamped  from  sheets 
of  boiler  steel.  Cast  iron  cannot  resist  bending  strains  as  well 
as  steel,  and  for  this  reason  steel  brackets  are  better  than  those 
made  of  cast  iron.  Brackets  are  usually  riveted  a  little  above 
the  middle  line  of  the  boiler  in  such  a  position  that  about  three- 
fifths  of  the  circumference  of  the  shell  will  be  below  them.  The 
boiler  shown  in  Fig.  5  is  fitted  with  brackets  of  a  shape  commonly 
used.  Small  boilers  are  provided  with  two  brackets  on  each 
side,  but  the  larger  sizes  have  three  brackets  on  each  side,  the 
middle  one  being  used  to  prevent  the  boiler  sagging  at  this  point. 

To  allow  for  free  expansion  of  the  boiler,  the  front  brackets 
usually  rest  directly  on  cast-iron  plates  placed  on  the  side  walls, 
and  the  rear  ones  rest  on  iron  rollers  placed  on  cast-iron  plates. 
This  anchors  the  front  end  so  it  cannot  move  and  leaves  the  rear 
end  free  to  move  and  take  up  expansion.  If  there  are  three 
brackets  0$  each  side,  both  the  middle  and  rear  ones  rest  on  rollers. 
The  principal  objection  to  supporting  boilers  by  means  of  brackets 
is  that  sometimes  t^ie  side  walls  will  settle  slightly  after  being- 
built  or  will  be  damagelfl?^  the  heat  to  which  they  are  subjected, 
thus  causing  twisting  strains  to  be  thrown  on  the  boiler. 

A  method  of  supporting  fire-tube  boilers  which  has  come  into 
extensive  use  in  recent  -years  is  illustrated  in  Fig.  94.  In  this 
method,  the  weight  of  the  boiler  i$  oot  carried  by  the  walls  of  the 
setting  but  by  steel,  columns  which  are  placed  in  the  outer  edge 
of  the  walls  and  which  rest  directly  on  the  foundation.  Steel 
channels  are  placed  back  to  back  across  the  boiler,  two  in  front 
and  two  at  the  rear,  and  rest  on  tap  of  the  side  columns.  Slings 
are  placed: between  the  channels  and  fastened  above  by  means  of 
heavy  cast-iron  washers  and  nuts,  and  the  boiler  is  hung  by  these 
slings,  which  are  fastened  to  the  lugs  with  pins.  Boilers  hung 
in  this  .manner  have  perfect-  freedom  for  expansion  without 
damage  to  the  brick  setting  and,  being  made  of  steel,  the  supports 
!are  not.  liable  to  break  as  easily  as  the  cast-iron  brackets,  nor 


202 


STEAM  BOILERS 


will  the  boiler  be  disturbed  if  the  walls  of  the  setting  should  settle. 
A  modification  of  the  above  method,  which  is  sometimes  used, 
is  to  support  the  rear  of  the  boiler  by  means  of  slings,  as  de- 
scribed above,  and  to  have  the  front  end  supported  by  brackets 
resting  on  cast-iron  plates  placed  on  the  wall  of  the  setting. 
This  method,  however,  has  few  of  the  advantages  of  support- 
ing entirely  by  slings  and  has  the  disadvantages  of  bracket 
supports. 


FIG.  94. — Fire-tube  boiler  with  Dutch  oven  setting. 

162.  Bridge  Wall. — The  bridge  wall  is  for  the  purpose  of 
preventing  the  coal  from  falling  off  the  grates  and  of  forcing  the 
air  to  pass  up  through  the  fuel  bed.  The  shape  of  the  wall, 
whether  flat  on  top  or  curved  to  correspond  with  round  shells, 
or  whether  with  vertical  or  with  sloping  sides,  appears  to  make 
little  difference  according  to  tests  made  by  Mr.  George  H.  Barrus. 
The  area  over  the  wall  must  be  large  enough  not  to  check  the  draft 
but,  beyond  that,  the  effects  of  shape  appear  to  be  slight.  A 
flat  wall  is  easier  to  build,  but  most  engineers  prefer  a  curved 
top  with  a  vertical  front  face,  and  with  the  upper  edge  cut  away 
at  an  angle  of  45  degrees. 

With  soft  coals  it  is  best  to  admit  some  air  above  the  grate  and 


SETTINGS  203 

for  that  purpose  the  bridge  wall  is  often  made  "split,"  that  is, 
hollow,  with  air  passages  in  its  back  face  or  on  top.  These 
passages  or  holes  may  be  made  in  a  cast-iron  plate  set  in  the 
bridge  wall,  or  be  made  between  the  bricks  by  spacing  them 
a  short  distance  apart.  The  hollow  center  of  the  wall  can  be 
connected  to  the  air  space  in  the  side  walls  of  the  setting  so  as 
to  draw  heated  air  only.  Fig.  95  illustrates  a  common  method 
of  constructing  a  split  bridge  wall.  The  air  supply  should  be 
easily  controlled  by  a  damper.  In  internally  fired  flues,  air 
may  be  passed  from  the  ash  pit  through  an  opening  in  the  plate 
beneath  the  bridge  wall,  which  opening  can  be  controlled  by  a 


FIG.  95. — Split  bridge  wall. 

slide  or  damper  door  easily  moved  from  the  front  by  the  slice 
bar  or  poker.  The  split  bridge  often  materially  assists  in  pre- 
venting the  generation  of  an  excess  of  smoke,  but  like  every 
other  such  device,  must  be  handled  with  intelligence. 

163.  Dutch  Ovens. — It  has  long  been  recognized  that  the 
setting  previously  described  for  return  fire-tube  boilers,  while 
substantial  and  giving  good  results  with  anthracite  coal,  is  not 
well  suited  for  burning  the  poorer  grades  of  bituminous  coal. 
Various  modifications  of  the  ordinary  setting  have  been  used  in 
an  effort  to  secure  better  combustion  of  the  cheaper  grades  of 
coal. 

One  of  the  most  common  of  these  is  the  Dutch  oven  setting 
shown  in  Fig.  94.  This  consists  of  an  extension  of  the  ordinary 
setting  built  out  in  front  of  the  boiler  and  containing  the  grates. 
The  extension  is  arched  over  and  lined  with  good  fire  brick  to 
resist  the  very  high  temperatures  which  exist  in  the  furnace. 
The  bridge  wall,  which  is  also  lined  with  fire  brick,  is  built  just 
back  of  the  furnace  and  has  a  sloping  face  for  directing  the  hot 
gases  against  the  boiler. 

The  principal  advantage  of  the  Dutch  oven  furnace  is  derived 
from  its  large  combustion  chamber  and  the  longer  path  which 
the  hot  gases  take  before  reaching  the  comparatively  cool  surfaces 


204 


STEAM  BOILERS 


of  the  boiler,  thus  allowing  a  better  opportunity  for  the  combus- 
tible gases  to  become  mixed  with  air  and  burned  at  a  high  tem- 
perature. These  results  are  not  always  obtained,  however,  as 
the  furnace  is  often  built  too  short.  Sometimes,  also,  the  draft 
used  is  so  strong  that  the  gases  are  taken  out  of  the  furnace  before 
they  have  mixed  and  burned. 

The  very  high  temperature  maintained  in  a  Dutch  oven  furnace 
causes  the  fire-brick  lining  to  burn  out  quickly,  making  it  ex- 
pensive to  maintain.  The  high  temperatures  require  that  the 
front  wall  be  thick,  which  makes  firing  rather  difficult.  Even 
with  the  objections  noted  above,  the  Dutch  oven  gives  much 
better  results  with  bituminous  coals  than  do  the  more  common 
forms  of  settings. 

164.  The  Chicago  Setting. — The  general  details  of  settings  for 
return  fire-tube  boilers,  recommended  by  the  Chicago  Depart- 
ment of  Smoke  Prevention,  are  shown  in  Figs.  96  and  97.  The 


FIG.  96. — Chicago  setting  with  single  door. 

setting  shown  in  Fig.  97  differs  from  that  shown  in  Fig.  96  in 
having  two  fire  doors  instead  of  one,  thus  allowing  one  side  of  the 
furnace  to  be  fired  at  a  time,  in  order  that  the  gases  being  distilled 
from  the  freshly  fired  charge  may  have  an  opportunity  to  mix  with 
the  hotter  gases  given  off  from  the  other  side  of  the  furnace. 

These  settings  differ  from  the  ordinary  setting  in  having  an 
arched  combustion  chamber  which  extends  from  the  front  of 
the  boiler  to  a  point  about  30  in.  beyond  the  bridge  wall.  The 


SETTINGS 


205 


arch  prevents  the  combustible  gases  from  coming  in  contact 
with  the  shell  of  the  boiler  before  they  have  had  an  oppor- 
tunity to  be  burned. 

After  passing  the  bridge  wall,  the  hot  gases  are  deflected 
downward  and  inward  by  another  arch,  thus  making  their  path 
longer  and  causing  them  to  remain  in  the  combustion  chamber 
a  greater  length  of  time. 

Regarding  the  construction  of  this  setting,  the  Department 
of  Smoke  Prevention  makes  several  recommendations,  among 
which  are  the  following: 

The  doors  should  be  provided  with  grids  for  admitting  air 
above  the  fire.  The  grids  should  have  an  area  of  at  least  4  sq. 
in.  for  each  square  foot  of  grate  surface. 


FIG.  97. — Chicago  setting  with  double  doors. 

The  arches  should  be  made  of  wedge  brick  and  not  of  two 
courses  laid  flat. 

The  bridge  wall  should  be  made  of  the  best  grade  of  fire 
brick  above  the  grate  line  and  faced  with  fire  brick  to  a  thickness 
of  9  in.  on  the  combustion  chamber  side.  The  bridge  wall  should 
not  extend  entirely  across  the  furnace,  in  order  to  allow  a  little 
space  for  expansion. 

The  combustion  chamber  floor  should  be  paved  with  fire 
brick  laid  on  edge. 

The  fire-brick  lining  below  the  spring  of  the   arches  should 


206 


STEAM  BOILERS 


be  not  less  than  9  in.  thick,  while  the  lining  above  the  arches  may 
be  4£  in.  thick  with  headers  every  fifth  row. 

The  fire  brick  over  fire  and  clean-out  doors  should  be  arched. 

The  thrust  of  the  arches  should  be  taken  up  by  a  piece  of 
metal  imbedded  in  the  outer  wall  of  the  setting,  directly  opposite 
the  point  where  the  arch  springs. 

Broad  flat  top  grates,  such  as  the  herringbone,  should  not 
be  used  with  bituminous  coal. 

Chimneys  less  than  75  ft.  above  the  grate  line  should  not 
be  used,  and  this  height  should  be  used  only  where  the  chimney  is 
connected  directly  to  the  boiler  uptake.  In  case  a  breeching 
and  detached  chimney  is  used,  add  to  the  height  of  the  chim- 
ney 10  ft.  for  every  turn  in  the  breeching  and  1  ft.  for  each 
foot  length  of  the  breeching. 

Although  the  Chicago  setting  is  more  complicated  than  the 
ordinary  setting,  it  has  the  advantage  of  requiring  no  more 
space  and  of  giving  good  results  when  handled  intelligently. 

165.  The  Burke  Furnace.— The  Burke  furnace  shown  in  Figs.  98 
and  99,  is  another  modification  in  the  ordinary  setting  designed 
to  burn  bituminous  coal  without  producing  smoke.  This  furnace 


FIG.  98. — Cross-section  of  Burke  furnace. 

is  built  in  the  form  of  a  Dutch  oven  extending  in  front  of  the 
boiler,  but  it  differs  from  the  ordinary  Dutch  oven  in  having 
three  sets  of  grate  bars.  The  grates  on  each  side  of  the  furnace 
are  of  the  ordinary  flat  type  and  are  inclined  toward  the  center 
of  the  furnace,  while  the  center  is  a  horizontal  shaking  grate. 
Coal  is  fed  to  the  sloping  grates  through  hoppers  in  the  top 
of  the  furnace,  thus  making  it  necessary  to  open  the  furnace 


SETTINGS 


207 


doors  frequently.  The  furnace  lining  is  cooled  and  prevented 
from  burning  by  circulating  air  around  it  through  spaces  built 
in  the  side  walls.  Air  enters  the  furnace  both  above  and  below 
the  grates,  that  entering  above  being  admitted  through  the  side 
walls.  This  furnace  resembles  some  forms  of  automatic  stokers 
but  differs  from  them  in  being  manipulated  by  hand. 


BOIL.E.* 


FIG.  99. — Longitudinal  section  of  Burke  furnace. 

166.  Back  Connections. — The  back  connection  of  a  boiler, 
which  extends  from  the  rear  head  to  the  rear  wall  of  the  setting, 
is  for  the  purpose  of  guiding  the  hot  gases  from  the  combustion 


FIG.  100. 


FIG.  101. 


chamber  into  the  tubes.  It  is  usually  constructed  in  one  of  the 
forms  shown  in  Figs.  100  and  101.  That  shown  in  Fig.  100  con- 
sists of  a  flat  cast-iron  plate  with  a  rib  on  the  back  to  strengthen 
it,  one  end  of  the  plate  resting  in  a  niche  in  the  rear  wall  of  the 


208 


STEAM  BOILERS 


setting  and  the  other  end  resting  on  a  2  in.'X2  in.  angle  riveted 
to  the  rear  head  of  the  boiler.  The  plate  is  covered  with  6  or  8  in. 
of  dry  dirt  or  sand  to  prevent  air  leaking  in  at  this  point  and 
also  to  prevent  the  escape  of  heat.  The  filling  should  be  done 
carefully,  as  air  leaking  into  the  setting  at  this  point  reduces 
the  draft  very  much.  The  plate  should  be  a  little  shorter  than 
the  distance  from  the  boiler  to  the  back  edge  of  the  niche  in  the 
setting  in  order  to  allow  free  expansion  of  the  boiler  without 
injuring  the  setting. 

The  form  of  back  connection  shown  in  Fig.  101  consists  of  a 
half  arch  sprung  from  the  back  wall  of  the  setting  to  the  rear 
head  of  the  boiler,  and  resting  on  an  angle  iron  riveted  to  the 
head.  The  arch  consists  of  cast-iron  skeleton  forms  filled  with 


FIG.  102. 

brick,  as  shown  in  Fig.  102,  laid  side  by  side  and  then  covered 
with  dry  dirt  or  sand.  As  in  the  plate  connection,  there  should 
be  a  little  space  between  the  head  of  the  boiler  and  the  arch  to 
allow  for  expansion. 

167.  Blow-Off  Connection. — Each  boiler  should  be  provided 
with  a  blow-off  connection  at  its  lowest  point,  for  draining 
the  boiler  and  blowing  out  the  mud  and  sediment  which  collects 
from  time  to  time.  Horizontal  boilers  are  set  with  the  rear  end 
1  or  2  in.  lower  than  the  front 'end  and  with  the  blow-off  con- 
nected to  the  bottom  of  the  shell  at  the  rear  end  as  in  Fig.  93.  It 
is  not  good  practice  to  connect  the  blow-off  into  the  head,  as  it 
has  to  be  placed  above  the  curvature  at  the  edge,  leaving  a 
depth  of  1  or  2  in.  from  which  the  water  cannot  be  drained. 
Mud  and  sediment  will  eventually  collect  at  this  point  and 
become  baked  on  the  plates,  leaving  them  in  condition  to  be 
burned  by  the  hot  gases  passing  underneath.  Water-tube 


SETTINGS 


209 


boilers  usually  have  a  mud  drum  placed  at  the  lowest  point  of 
the  boiler,  and  the  blow-off  is  connected  to  this. 

The  bottom  blow-off  should  be  of  extra  heavy  pipe,  1J  in. 
in  diameter  for  boilers  up  to  42  in.  in  diameter,  2  in.  for  44  to 
60-in.  boilers  and  2J  in.  for  boilers  of  larger  size.  When 
using  the  bottom  blow-off,  the  velocity  of  the  water  flowing 
through  the  pipe  should  be  sufficient  to  keep  the  mud  and 


FIG.  103. — Cast-iron  blow-off  pipe. 

scale  moving,  otherwise  these  are  apt  to  collect  at  the  bend 
and  clog  the  pipe.  For  this  reason  the  valve  in  the  blow-off  pipe 
should  be  opened  wide  when  blowing. 

When  the  blow-off  pipe  is  2  in.  or  larger  in  size,  the  shell 
should  be  reinforced  with  a  plate  at  the  point  where  the  pipe 
enters  the  boiler,  and  the  tapping  should  be  done  through  both 
the  plate  and  shell.  Another  way  of  reinforcing  the  shell  is  to 
rivet  a  tapped  pipe  flange  to  the  shell. 


ooooooo 
ooooooo 
ooooooo 
ooooooo 


FIG.  104. 

In  some  cases  it  is  desirable  to  carry  the  blow-off  pipe  out 
of  the  setting  above  the  level  of  the  floor  of  the  combustion 
chamber.  Where  this  is  done,  the  connection  should  be  made 
with  a  heavy  cast-iron  pipe  of  the  form  shown  in  Fig.  103.  Some 
boiler  manufacturers  furnish  such  pipe  for  this  purpose.  A 
horizontal  blow-off  should  not  be  used  if  it  can  be  avoided.  It 
is  better  to  run  the  blow-off  pipe  vertically  to  a  point  below  the 


210 


STEAM  BOILERS 


floor  of  the  combustion  chamber  and  then  carry  it  outside  the 
setting  with  an  easy  bend. 

Whether  the  blow-off  pipe  is  horizontal  or  vertical,  it  should 
be  well  protected  from  the  action  of  the  hot  gases.  Since  the 
blow-off  valve  is  placed  outside  the  setting,  the  pipe  is  full  of 
still  water.  Sediment  will  settle  out  of  still  water  much  quicker 
than  when  the  water  is  in  circulation,  and  as  heat  hastens  the 
deposit  of  certain  kinds  of  sediment,  the  blow-off  pipe  is  apt  to 
have  sediment  baked  to  it  if  it  is  left  unprotected  in  the  path  of 
the  hot  gases  leaving  the  furnace. 


WATER      LEVEL 


FIG.  105. 


A  good  form  of  protection  for  a  horizontal  blow-off  pipe  is 
shown  in  Fig.  104,  which  consists  of  a  narrow  brick  pier  resting 
on  the  floor  of  the  combustion  chamber  and  having  its  top  en- 
closing the  blow-off  pipe.  As  the  pier  is  only  8  in.  wide,  it  does 
not  interfere  materially  with  the  passage  of  the  flue  gases. 
Wherever  brick  protection  of  the  blow-off  is  used,  the  brick- 
work should  not  be  brought  right  up  to  the  shell,  as  this  promotes 
external  corrosion  of  the  shell,  nor  should  the  brickwork  be 
joined  to  the  shell  by  means  of  mortar  for  the  same  reason, 
since  the  lime  in  the  mortar  absorbs  moisture.  Fire  clay  or  red 
lead  are  better  materials  for  this  purpose. 

A  good  protection  for  a  vertical  blow-off  pipe  may  be  made 
by  placing  around  the  part  of  the  blow-off  pipe  which  passes 
through  the  combustion  chamber,  a  sleeve,  made  of  glazed  tile 
or  cast-iron  pipe  2  or  3  in.  larger  in  diameter  than  the  blow-off 
pipe  itself,  and  packing  the  space  between  these  pipes  with  some 
heat-resisting  substance,  such  as  asbestos.  A  fairly  good  protec- 
tion may  be  constructed  by  building  a  V-shaped  brick  pier  imme- 


SETTINGS 


211 


diately  in  front   of   the   blow-off   pipe,    as   shown  in  Figs.  96 
and  97. 

In  some  cases  the  hot  gases  passing  through  the  combustion 
chamber  have  a  very  high  temperature,  as  where  forced  draft  is 
used.  If  such  is  the  case,  and  the  boiler  is  not  blown  off  fre- 
quently, it  is  desirable  to  run  a  circulating  pipe  from  a  point  in 
the  blow-off  pipe  outside  the  end  wall  to  a  point  in  the  rear  head 
of  the  boiler  just  below  the  water  line,  as  shown  in  Fig.  105,  each 


-U^U 

3OOOT%m 

OOOO 
OOOO 
OOOO 
O 


FIG.  106. — Buck-stay. 

pipe  being  provided  with  a  valve.  A  continuous  circulation  will 
then  take  place  through  the  blow-off  and  the  circulating  pipes 
and  there  will  be  no  danger  of  overheating.  If  this  arrangement 
is  used,  it  will  not  be  necessary  to  place  a  protecting  covering 
around  the  blow-off  pipe.  In  blowing  off  the  boiler,  the  valve 
in  the  circulating  pipe  should  be  closed;  at  all  other  times  it 
should  be  left  open. 

When  boilers  are  placed  in  batteries,  the  blow-off  from  each 
boiler  in  a  battery  may  be  connected  outside  the  setting  to  a 

19 


212  STEAM  BOILERS 

common  blow-off  pipe  passing  in  the  rear  of  all  the  boilers,  each 
branch  being  provided  with  its  own  valve. 

168.  Buck-stays. — Buck-stays  are  used  to  brace  the  side  walls 
of  a  setting  to  prevent  their  spreading.     They  are  usually  made 
of  cast  iron  with  a  heavy  web  on  the  back,  as  shown  in  Fig.  106. 
The  web  is  made  about  4  or  5  in.  wide  and  about  1  in.  thick, 
like   the   other   part   of   the   buck-stay.     These  buck-stays  are 
placed  every  5  or  6  ft.  along  the  side  walls,  and  those  on  opposite 
sides  of  the  setting  are  connected  by  long  bolts  passing  entirely 
through  the  setting  at  the  top  and  bottom. 

169.  Water-tube  Boiler  Settings. — Nearly  every  type  of  water- 
tube  boiler  has  a  different  form  of  setting,  so  that  very  little 
information  of  a  general  nature  concerning  them  can  be  given. 
The  different  forms  of  settings  for  these  boilers  may  be  seen  in 
the  illustrations  given  in  Chapter  II. 

In  general,  those  water-tube  boilers,  which  have  small,  hori- 
zontal steam  drums  and  sectional  headers,  are  supported  by 
bands  which  pass  under  the  steam  drums  and  are  fastened  to 
slings,  which  are  in  turn  suspended  from  beams  passing  across 
the  top  of  the  boiler  and  resting  on  columns  imbedded  in  the 
side  walls.  This  relieves  the  setting  from  carrying  the  weight 
of  the  boiler  and  at  the  same  time  allows  freedom  for  expansion. 
Those  boilers  which  have  horizontal  steam  drums  and  have  the 
headers  made  from  steel  plates  are  usually  supported  by  the 
bottoms  of  the  headers,  resting  directly  on  the  front  and  rear 
walls,  although  they  are  sometimes  suspended  by  slings  and 
bands.  For  vertical  boilers,  the  setting  is  generally  cylindrical 
in  shape  with  the  furnace  at  the  bottom,  the  boilers  being  sup- 
ported directly  on  foundation  walls  beneath  them.  All  water- 
tube  boiler  settings  are  lined  with  fire  brick  wherever  the  hot 
gases  come  in  contact  with  the  setting. 

The  principal  objection  to  the  ordinary  forms  of  settings  for 
water-tube  boilers  is  that  it  is  practically  impossible  to  burn 
bituminous  coal  in  them  without  producing  smoke.  Various 
modifications  have  been  made  in  the  settings  to  secure  more 
complete  and  smokeless  combustion  of  these  cheaper  grades  of 
coal.  These  modifications  may  be  divided  into  three  classes, 
namely,  the  addition  of  a  Dutch  oven  to  the  furnace,  the  rear- 
rangement of  the  passes  and  the  covering  of  the  lower  tubes  with 
tile,  and  a  rearrangement  of  the  setting  to  secure  better  mixing 
of  the  volatile  gases  and  air. 

The  Dutch  oven  furnace  has  been  described  in  connection 


SETTINGS 


213 


with  fire-tube  boiler  settings  and  needs  no  further  attention  here, 
as  the  furnace  is  the  same  whether  applied  to  a  fire-  or  water-tube 
boiler.  As  applied  to  water-tube  boilers,  it  is  usually  equipped 
with  a  mechanical  stoker  which  may  be  of  any  of  the  types  pre- 
viously described.  The  more  common  arrangements  of  the  passes 
and  the  uses  of  tile  covering  for  the  tubes  have  also  been  described 
in  Chapter  XII  on  smokeless  combustion. 

170.  The  Kent  Wing  Wall  Setting. — One  of  the  settings  very 
commonly  used  for  water-tube  boilers  and  designed  to  produce 


FIG.  107. — Kent  wing  wall  setting. 

smokeless  combustion  is  known  as  the  Kent  Wing  Wall  Furnace, 
illustrated  in  plan  and  section  in  Fig.  107.  This  setting  consists 
of  a  Dutch  oven  lined  with  fire  brick  and  provided  with  two 
doors  for  alternate  firing.  Just  back  of  the  bridge  wall  are  two 
wing  walls,  E,  one  on  each  side,  projecting  toward  the  center 
of  the  setting,  and  immediately  back  of  these  are  a  series  of 


214 


STEAM  BOILERS 


baffles  H,  built  of  fire  brick.  In  operation,  coal  is  spread  evenly 
over  only  one-half  of  the  furnace  at  each  firing,  and  a  large  excess 
of  air  is  admitted  over  the  bed  of  fuel  on  the  other  half  of  the 
grate.  The  volatile  gases  distilled  from  the  freshly  fired  fuel, 
and  the  air  passing  over  the  other  half  of  the  fire,  are  both  forced 
to  pass  through  the  narrow  opening  between  the  wing  walls, 

UPTAXE-. 


FIG.  108. — Wooley  smokeless  setting. 

where  they  are  thoroughly  mixed.  The  baffles  H,  serve  to 
further  mix  the  gases  and  air,  although  their  principal  office  is  to 
store  up  heat  when  the  furnace  is  hottest  and  give  it  out  again 
when  the  temperature  is  lower.  The  good  results  obtained  by 
the  use  of  the  Kent  Wing  Wall  Setting  are  due  largely  to  the 
roomy  combustion  chamber,  the  thorough  mixing  of  combus- 


SETTINGS  215 

tible  gases  and  air,  and  the  length  of  time  before  the  gases  come 
in  contact  with  the  cooler  boiler  tubes. 

171.  The  Wooley  Smokeless  Setting.— The  Wooley  Smokeless 
setting  shown  in  Fig.  108  is  another  form  commonly  used  with 
water-tube  boilers.     This  setting  consists  of  a  Dutch  oven  with 
a  dividing  wall  down  the  center,  wing  walls  built  on  top  of  the 
bridge  walls,  and  a  deflecting  wall  inside  the  combustion  chamber. 
This  furnace  is  intended  to  be  fired  alternately,  and  the  com- 
bustible gases   and  air  are  both  forced    to    pass    though  the 
narrow  opening  between  the  wing  walls.     This  opening,    though 
narrow,  has  sufficient  area  to  avoid  reducing  the  draft.     The 
deflecting  wall  causes  the  paths  of  the  gases  from  each  side  of 
the  furnace  to  cross  as  they  pass  between  the  wing  walls,  thus 
insuring  a  thorough  mixing.     The  lower  row  of  water  tubes  is 
covered  with  fire  tile  between  the  Dutch  even  and  the  deflecting 
wall,   and  the  hot  gases  pass  beneath  the  deflecting  wall  in 
leaving  the  furnace,  thus  giving  them  a  longer  path  before  they 
reach  the  tubes. 

172.  Steel  Settings. — Steel  boiler  settings  have  been  used  in 
some  cases  instead  of  the  ordinary  brick  setting.     Steel  settings 
consist  of  an  outer  casing  of  sheet  steel,  riveted  together  and 
stiffened  with  angle  irons  or  tee  bars.     The  sheet  steel  is  lined 
with,  first,  a  thickness  of  asbestos  over  which  is  placed  a  layer  of 
red  clay  and  then  a  layer  of  fire  clay.     The  principal  advantages 
of  these  settings  is  that  they  are  practically  air  tight,  and  that 
they  are  not  injured  by  the  continual  expansion  and  contraction 
of  the  boiler,  nor  from  settling  of  walls  as  is  sometimes  the  case 
with  brick  settings.     Their  cost  is  about  the  same  as  for  brick 
settings. 

173.  Shaking  Grates. — Shaking  or  rocking  grates  are  for  the 
purpose  of  cleaning  the  fires  and  removing  ashes  without  the 
necessity  for  opening  the  furnace  doors.     In  order  to  accomplish 
this  purpose,  the  grate  bars  consist  of  a  number  of  small  movable 
sections  as  shown  in  Fig.  109.     The  grate  bars  are  connected  to 
rods  which  extend  to  the  front  of  the  furnace  and  are  there  joined 
to  levers  by  which  they  may  be  given  the  desired  motion.     By 
moving  the  levers  slightly,  the  grate  bars  are  given  a  gentle  up- 
and-down  motion  which  is  sufficient  to  remove  the  ashes  without 
disturbing  the  fire  very  much.     Should  clinkers  collect,  or  the 
coal  cake,  the  fire  may  be  thoroughly  stirred  and  the  clinkers 


216  STEAM  BOILERS 

broken  by  giving  a  larger  motion  to  the  grate  bars,  as  illustrated 
by  the  front  section  of  the  grate  shown  in  Fig.  109. 

Since  shaking  grates  render  unnecessary  the  continual  opening 
of  furnace  doors  to  trim  the  fires,  they  promote  efficiency  and 
smokeless  combustion  by  preventing  too  much  cold  air  from 
entering  the  furnace.  They  also  lighten  the  labor  of  the  fire- 
man, as  one  of  the  hardest  tasks  he  has  to  perform  is  that  of 
standing  in  the  hot  glow  from  the  furnace  and  slicing  the  fire. 


FIG.  109. — Shaking  grates. 

174.  Grate  Bars. — Grates  are  usually  made  of  cast  iron  in  the 
form  of  bars  or  sections  which  fit  together  to  make  up  the  entire 
grate,  the  bars  being  made  up  of  alternate  " lands"  for  the  sup- 
port of  the  fuel  and  openings  for  the  admission  of  air.  The  most 
common  forms  of  grate  bars  are  the  Plain,  the  Tupper,  the 
Herringbone,  and  the  Pinhole,  shown  in  Fig.  110.  The  Tupper 
and  Herringbone  grates  are  suitable  for  burning  anthracite  and 
the  free  burning  varieties  of  bituminous  coals,  but  are  not 
adapted  to  caking  coals  or  those  which  clinker,  as  the  clinker 
adheres  to  them  and  it  is  hard  to  run  a  slice-bar  under  the  fire 
for  breaking  the  clinker.  The  plain  grate  is  best  adapted  for 
these  coals,  as  there  is  a  small  groove  along  the  top  of  each  bar 
which  soon  fills  with  ash  and  prevents  clinkers  from  adhering. 
A  pointed  bar  may  be  easily  run  under  the  fire  along  this  groove, 
making  it  easy  to  slice  the  fire.  Pinhole  grates  are  particularly 
adapted  to  burning  sawdust  and  other  refuse  matter. 

The  openings  in  grates  vary  from  1/4  in.  to  5/8  in.  in  width, 
depending  on  the  size  of  coal  to  be  used.  The  openings  should 
be  narrowest  at  the  top  of  the  grate  and  widen  toward  the 
bottom  in  order  to  prevent  their  being  stopped  up  by  small 


SETTINGS 


217 


pieces  of  coal  or  coke.  The  open  spaces  should  constitute  one- 
half  of  the  total  area  of  the  grate  in  order  to  admit  sufficient  air 
for  combustion,  but  if  they  constitute  a  greater  proportion  of  the 
area  than  this,  too  much  air  will  be  admitted  and  the  efficiency 
of  the  furnace  lowered. 

A  web  should  be  cast  on  the  under  side  of  each  grate  bar, 
to  give  it  greater  strength  to  support  the  fuel  and  also  to  give  it 


Plain  grate  bar. 


Tupper  grate  bar. 


Herringbone  grate  bar. 


ooooooooooooooooooooooooooooooo 

oooooooooooooooooooooooooooooo 

ooooooooooooooooooooooooooooooo 


an  h 

°y  v 


Pinhole  grate  bar. 
FIG.  110. 

enough  stiffness  to  prevent  its  being  warped  by  the  heat  to  which 
it  is  exposed.  If  the  web  has  a  depth  of  about  4  in.  there  will  be 
little  danger  of  its  breaking,  even  if  the  top  becomes  red  hot. 
Grate  bars  are  usually  made  in  lengths  of  3  ft.,  and  the  total 
length  of  the  grate  will  then  be  some  multiple  of  3.  The  most 
common  length  of  grate  for  bituminous  coal  is  6  ft.  A  greater 


218  STEAM  BOILERS 

length  than  this  cannot  be  sliced  very  easily,  and  ashes  are  apt  to 
accumulate  near  the  bridge  wall.  If  a  dead  plate  is  used  for 
caking  the  coal,  it  will  add  about  1  ft.  to  the  furnace,  making 
its  entire  length  7  ft.  Grates  for  burning  anthracite  coal  may 
have  a  length  of  9  ft.,  as  this  kind  of  coal  does  not  require  slicing. 
Grates  for  this  kind  of  coal  are  sometimes  made  12  ft.  long,  but 
this  is  not  advisable  as  it  is  very  difficult  for  a  fireman  to  throw 
coal  so  far  and  place  it  just  where  it  should  be.  The  grates 
should  be  given  a  slope  of  1  in.  in  20  toward  the  bridge  wall 
in  order  to  'make  it  easier  to  throw  coal  to  the  back  of  the  furnace. 
The  principal  cause  of  the  destruction  of  grates  is  the  con- 
tinuous heat  to  which  they  are  subjected.  The  lack  of  a  proper 
flow  of  air  through  the  grates  will  quickly  cause  overheating  and 
burning.  The  flow  of  air  may  be  retarded  or  stopped  by  the 
openings  becoming  clogged  with  ashes  or  by  the  openings  being 
too  small.  Another  fruitful  source  of  burned  grate  bars  is  an 
accumulation  of  ashes  in  the  ash  pit.  These  ashes,  being  hot, 
will  heat  the  air  passing  over  them  and  will  restrict  its  amount 
until  the  grates  are  not  cooled  sufficiently  and  they  will  be 
burned.  The  remedy  for  this  is,  of  course,  to  keep  the  ash  pit 
cleaned. 


CHAPTER  XIV 
PIPING  AND  BOILER  FITTINGS 

175.  Kinds  of  Pipe. — Pipes  used  for  conveying  steam  are  made 
either  of  steel  or  wrought  iron,  except  in  a  few  special  cases 
where  copper  pipe  is  used.  By  far  the  larger  part  of  the  piping 
erected  to-day  is  of  steel,  as  this  is  cheaper  than  wrought  iron. 
Wrought-iron  pipe  wears  better  than  steel  as  it  is  not  so  subject 
to  corrosion,  and,  as  it  is  softer,  it  may  be  threaded  more  perfectly 
and  with  greater  ease  than  the  steel  pipe.  Very  few  companies 
are  now  manufacturing  wrought-iron  pipe,  though  a  number  of 
them  sell  steam  pipe  which  is  branded  as  wrought  iron.  Steel 
pipe  is  not  so  easily  welded  as  wrought  iron,  hence,  it  is  often 
poorly  welded  and  is  apt  to  split,  though  great  improvement  in 
this  respect  has  been  made  by  the  manufacturers  in  recent  years. 

Each  length  of  pipe  as  sold  is  threaded  on  both  ends  and  is 
provided  with  a  coupling  or  collar  screwed  on  one  end.  There 
is  no  standard  length  for  pipe,  the  range  of  length  usually  being 
from  16  to  24  ft.,  with  occasional  short  pieces.  It  can  be  ordered 
in  lengths  cut  as  desired  for  a  slight  increase  in  price,  but  it  can 
be  readily  cut  to  any  length  and  threaded  by  a  pipe  fitter.  The 
pipe  now  made  by  manufacturers  is  of  standard  size  so  that  pipe 
obtained  from  one  manufacturer  is  reasonably  certain  to  fit 
that  made  by  another  firm. 

Both  wrought  iron  and  steel  pipe  are  quite  malleable  and,  when 
heated,  may  be  readily  bent  to  almost  any  shape  by  a  skillful 
workman  without  materially  changing  the  form  of  the  cross- 
section.  It  is  not  a  good  plan  to  bend  pipe  while  cold,  on  account 
of  the  liability  of  splitting  the  joint  or  seam  and  also  the  danger 
of  changing  the  cross-section,  though  the  latter  may  be  pre- 
vented by  inserting  a  coil  spring  of  the  same  size  as  the  pipe 
or  by  filling  the  pipe  with  sand  before  attempting  to  bend  it. 

Merchant  pipe  is  a  term  used  to  designate  regular  pipe  of  the 
market,  and  orders  are  filled  with  this  kind  unless  otherwise 
specified  in  the  order.  Merchant  pipe  will  weigh  from  5  to  10 
per  cent  less  than  the  weights  given  in  the  following  table  of 
dimensions  of  standard  pipe.  When  full  weight  pipe  is  required 

219 


220 


STEAM  BOILERS 


the  order  should  state  this  fact.  Full  weight  pipe  will  weigh 
as  much  or  a  little  more  than  the  weights  given  in  the  table  below. 
Pipe  is  manufactured  in  three  regular  thicknesses  or  weights, 
called  respectively  Standard,  Extra  Strong,  and  Double  Extra 
Strong.  Standard  pipe  has  the  dimensions  and  weights  given 
in  the  following  table  and  is  suitable  for  pressure  up  to  125  Ib. 
per  sq.  in. 

TABLE  OF  DIMENSIONS  OF  STANDARD  STEAM  PIPE 

1  1  and  Smaller  Proved  to  300  Ib.  per  sq.  in.  by  Hydraulic  Pressure. 
1  %  and  Larger  Proved  to  500  Ib.  per  sq.  in.  by  Hydraulic  Pressure. 


Nominal 
inside 
diame- 
ter 

Actual 
outside 
diame- 
ter 

Thick- 
ness 

Actual 
inside 
diame- 
ter 

Inside 
circum- 
ference 

Outside 
circum- 
ference 

Inside 
area 

Length 
of  pipe 
contain- 
ing 1  cu. 
ft. 

Weight 
per  foot 

No.  of 
threads 
per 
inch  of 
screw 

Square 

Inches 

Inches 

Inch 

Inches 

Inches 

Inches 

Inches 

Feet 

Lb. 

1/8 

0.405 

0.068 

0.270 

0.848 

1.272 

0.0572 

2500 

0.243 

27 

1/4 

0.54 

0.088 

0.364 

1.144 

1.696 

0.1041 

1385 

0.422 

18 

3/8 

0.675 

0.091 

0.494 

1.552 

2.121 

0.1916 

751.5 

0.561 

18 

1/2 

0.84 

0.109 

0.623 

1.957 

2.652 

0.3048 

472.4 

0.845 

14 

3/4 

1.05 

0.113 

0.824 

2.589 

3.299 

0.5333 

270 

1.126 

14 

1 

1.315 

0.134 

1.048 

3.292 

4.134 

0.8627 

166.9 

1.670 

11  1/2 

1  1/4 

1.66 

0.140 

1.380 

4.335 

5.215 

1.496 

96.25 

2.258 

11  1/2 

1  1/2 

1.90 

0.145 

1.611 

5.061 

5.969 

2.038 

70.65 

2.694 

11  1/2 

2 

2.375 

0.154 

2.067 

6.494 

7.461 

3.355 

42.36 

3.600 

11  1/2 

2  1/2 

2.875 

0.204 

2.468 

7.754 

9.032 

4.783 

30.11 

5.773 

8 

3 

3.50 

0.217 

3.067 

9.636 

10.996 

7.388 

19.49 

7.547 

8 

3  1/2 

4.00 

0.226 

3.548 

11.146 

12.566 

9.887 

14.56 

9.055 

8 

4 

4.50 

0.237 

4.026 

12.648 

14.137 

12.730 

11.31 

10.66 

8 

4  1/2 

5.00 

0.246 

4.508 

14.153 

15.708 

15.939 

9.03 

12.34 

8 

5 

5.563 

0.259 

5.045 

15.849 

17.475 

19.990 

7.20 

14.50 

8 

6 

6.625 

0.280 

6.065 

19.054 

20.813 

28.889 

4.98 

18.767 

8 

7 

7.625 

0.301 

7.023 

22.063 

23  .  954 

38.737 

3.72 

23.27 

8 

8 

8.625 

0.322 

7.982 

25.076 

27.096 

50.039 

2.88 

28.177 

8 

9 

9.625 

0.344 

9.001 

28.277 

30.233 

62.722 

2.26 

33.70 

8 

10 

10.75 

0.366 

10.019 

31.475 

33.772 

78.838 

1.80 

40.06 

8 

11 

11.75 

0.375 

11.00 

35.343 

36.91 

95.03 

1.455 

45.95 

8 

12 

12.75 

0.375 

12.000 

38.264 

40  .  840 

113.09 

1.235 

48.98 

8 

Extra  Strong  pipe  is  made  in  sizes  from  1/8  in.  to  8  in.  The 
ends  are  not  threaded  and  supplied  with  couplings,  as  with 
Standard  pipe  unless  specified  when  ordered.  Extra  strong 
pipe  differs  from  Standard  in  having  a  greater  thickness  of  walls. 
The  ouside  diameter  is  the  same  as  that  of  Standard  pipe,  there- 
fore, it  can  be  joined  to  the  Standard  pipe,  but  its  inside  diameter 
is  smaller.  It  is  suitable  for  steam  pressures  up  to  250  Ib.  per 
sq.  in. 


PIPING  AND  BOILER  FITTINGS  221 

Double  Extra  Strong  pipe  has  the  same  outside  diameter  as 
Standard  pipe  but  its  walls  are  even  thicker  than  the  Extra 
Strong,  thus  requiring  that  its  inside  diameter  be  less  than  that 
of  the  Extra  Strong.  It  is  suitable  for  pressures  up  to  800  Ib. 
per  square  inch.  To  illustrate  the  difference  in  sizes  of  the  three 
grades  of  pipe,  the  above  table  shows  that  a  1-in.  pipe  has  an 
outside  diameter  of  1.315  in.  and  an  inside  diameter  of  1.048  in. 
Extra  Strong  pipe  of  the  same  number  has  an  outside  diameter 
of  1.315  in.  and  an  inside  diameter  of  0.951  in.  Double  Extra 
Strong  pipe  of  the  same  number  has  an  outside  diameter  of 
1.315  in.  and  an  inside  diameter  of  0.587  in.  The  outside  diame- 
ters of  different  grades  of  pipe  are  made  the  same  in  order  that 
the  different  grades  may  be  joined  together.  It  will  be  seen 
from  the  above  table  that  the  size  of  a  pipe  refers  to  its  inside 
diameter,  even  though  its  inside  diameter-is  not  exactly  the  size 
number. 

Pipes  larger  than  12  in.  diameter  are  referred  to  as  0.  D.  pipe, 
meaning  that  the  size  number  refers  to  the  outside  diameter. 
O.  D.  pipe  is  made  in  thicknesses  from  1/4  in.  to  3/4  in.  and  in 
ordering  it  is  necessary  to  specify  the  thickness  wanted.  If  it  is 
desired  to  have  this  pipe  threaded  it  should  be  so  stated  on  the 
order.  In  this  connection  it  should  be  remembered  that  5/ 16  in. 
thickness  is  the  lightest  that  can  be  threaded.  Thinner  O.  D. 
pipe  than  this  should  be  provided  with  flanges. 

176.  Determining  the  Sizes  of  Pipes. — In  the  design  of  a  steam 
plant  no  detail  deserves  more  careful  attention  than  the  steam 
piping.  Not  only  is  this  fact  often  overlooked,  but  the  evils 
resulting  from  poor  design  are  usually  attributed  to  other  parts 
of  the  equipment. 

The  nature  of  the  substance  to  be  conveyed  by  the  pipe  must 
be  considered,  as  the  requirements  for  steam  are  entirely  different 
from  those  for  water,  oil,  air,  or  gas.  The  principles  governing 
steam-pipe  design  are:  (1)  The  moment  steam  leaves  the  boiler 
it  loses  heat  and  some  of  it  will  condense.  (2)  Water  of  conden- 
sation is  an  evil  and,  since  its  formation  cannot  be  prevented,  a 
perfect  pipe  system  must  provide  means  for  its  removal  as  fast 
as  it  is  formed.  (3)  There  can  be  no  flow  of  steam  without  a 
corresponding  drop  of  pressure.  (4)  Drop  of  pressure  of  steam 
does  not  cause  corresponding  loss  of  energy.  (5)  The  mechanical 
design  must  provide  ample  strength,  provision  for  expansion, 
and  properly  located  valves  of  suitable  design. 


222  STEAM  BOILERS 

The  proper  size  of  steam  pipe  to  use  in  any  case  may  be  calcu- 
lated from  the  following  formulas.  While  these  formulas  are 
somewhat  complicated  they  are  given  because  they  have  been 
tested  by  comparison  with  measurements  made  on  many  actual 
piping  systems. 


p=.  0003167^  (1) 

(2) 
(3) 

(4) 

in  which  p  is  the  loss  of  pressure  in  pounds  per  square  inch 
W  is  the  weight  of  steam  flowing  in  pounds  per  minute 
L    is  length  of  pipe  in  feet 
D    is  diameter  of  pipe  in  inches 
d     is  density  of  steam  in  pounds  per  cubic  foot 
V   is  velocity  of  steam  in  feet  per  minute. 
To  illustrate  the  use  of  some  of  these  formulas,  suppose  we  wish 
to  find  the  drop  in  pressure  in  a  3-in.  steam  line  150  ft.  long  which 
carries  3600  Ib.  of  steam  per  hour  at  a  pressure  of  106  Ib.  per 
sq.   in.  absolute.     The   density  of   this   steam  is   found    from 
the  steam  table  to  be  0.2425  and  the  weight  flowing  per  minute 

QfiOO 

is -°jp  =  60  Ib.  therefore, 

p=. 0003167x^—^  =  2.9  Ib.  nearly. 

If  we  wish  to  find  the  diameter  of  pipe  that  would  carry  the 
above  steam  with  a  drop  of  pressure  of  only  1  Ib.  per  square  inch 
we  would  substitute  in  the  third  formula  above 


602X150 
1x72425 


The  most  useful  of  the  above  formulas  are  the  second  and  third. 
The  second  is  used  when  we  wish  to  find  the  amount  of  steam 


PIPING  AND  BOILER  FITTINGS 


223 


that  will  flow  through  a  pipe  of  a  given  size  and  the  third  is  used 
when  we  want  to  find  the  size  of  pipe  needed  for  a  given  amount 
of  steam.  The  pressure  drop  p  allowed  is  usually  about  1  Ib. 
per  100  ft.  of  pipe,  though  this  may  be  altered  by  special 
conditions. 

177.  Expansion. — Most  of  the  breaks  that  occur  in  steam  pipes 


FIG.  111. — Slip  expansion  joint. 

are  breaks  around  the  pipe  near  a  joint.  This  indicates  that 
these  breaks  are  due  to  the  expansion  or  contraction  of  the  pipe. 
A  break  caused  by  excessive  pressure  within  the  pipe  would 
run  lengthwise  of  the  pipe. 


. 


FIG.  112. — Wainwright  expansion  joint. 

Ample  provision  should  be  made  in  all  steam  lines  to  allow  for 
expansion  and  contraction  in  such  manner  as  not  to  strain  the 
pipe.  About  the  simplest  method  of  allowing  for  expansion  is 
to  provide  elbows  in  the  line  with  long  legs  on  both  sides  of  them. 


224 


STEAM  BOILERS 


The  expansion  in  one  leg  will  be  taken  up  by  the  swing  of  the 
other  leg  which  is  at  right  angles  to  it.  If  high  steam  pressures 
are  to  be  carried,  a  better  method  is  to  use  long  easy  bends 
rather  than  elbows.  In  designing  these  bends  it  should  be 
borne  in  mind  that  the  thicker  the  pipe  the  longer  should  be  the 
radius  of  the  bend. 

In  the  case  of  a  long  straight  pipe  where  a  bend  or  elbow  cannot 
be  used  to  take  up  the  expansion,  it  is  common  to  use  some 
form  of  slip  joint  such  as  that  shown  in  Fig.  111.  These  ex- 
pansion joints  are  made  to  take  up  from  3  to  6  in.  of  expansion, 
and,  as  there  is  approximately  1  in.  of  expansion  in  50  ft.  of 


FIG.  113. 


FIG.  114. 


pipe,  an  expansion  joint  should  be  placed  every  150  to  300  ft. 
In  placing  this  type  of  joint  in  a  line  of  pipe  it  should  be  remem- 
bered that  there  is  nothing  to  prevent  the  joint  pulling  apart  and 
for  this  reason  great  care  should  be  used  to  firmly  anchor  the 
pipe  at  the  proper  distance  from  the  joint.  Some  expansion 
joints  cf  this  type  are  provided  with  long  bolts  which  pass 
through  both  end  flanges  with  a  nut  on  each  end.  This  pre- 
vents the  joint  coming  apart  in  case  of  excessive  contraction. 
The  packing  in  the  type  of  expansion  joint  shown  in  Fig.  Ill 
gives  some  trouble  when  used  on  high  pressure  lines  but  for 
ordinary  work  it  is  very  satisfactory. 

Another  type  of  expansion  joint  suitable  for  line  pipe  where 
space  is  limited  is  shown  in  Fig.  112.  This  consists  of  an  outer 
casing  of  corrugated  metal  provided  with  strengthening  bands  of 
steel  passing  around  it  and  with  flanges  at  the  ends.  An  inner 
casing  of  polished  steel  is  provided  for  reducing  friction  of  the 
steam.  Expansion  is  taken  up  by  stretching  the  corrugated 


PIPING  AND  BOILER  FITTINGS  225 

casing.     In  this  type  of  expansion  joint  no  trouble  is  experienced 
with  packing  or  with  the  joint  pulling  apart. 

In  line  piping  carrying  high  pressures,  an  excellent  method  of 
providing  for  expansion  is  by  inserting  a  bend,  such  as  shown  in 
Fig.  113  in  the  pipe  line.  Expansion  will  then  be  taken  up  by 
the  spring  of  the  bend.  Such  a  bend  should  be  made  of  heavy 
pipe  and  the  flanges  fastened  securely,  preferably  by  welding, 
as  expansion  brings  very  heavy  strains  on  them.  In  order  to 
prevent  the  bend  stopping  the  drainage  of  condensation  it 
should  be  turned  down  to  a  horizontal  position  or  the  pipe  line 
should  slope  away  from  it  on  either  side.  A  90  degree  bend  of  the 


FIG.  115. 

same  kind  is  shown  in  Fig.  114.  This  kind  is  used  very  com- 
monly in  connecting  each  boiler  of  a  battery  to  a  steam  main 
which  passes  across  all  the  boilers  in  the  battery. 

In  low-pressure  piping  systems,  such  as  those  used  for  heating, 
expansion  can  be  taken  up  by  constructing  an  off-set  in  the  pipe 
line  by  means  of  elbows  and  short  lengths  of  pipe,  as  shown  in 
Fig.  115.  This  device  takes  up  the  expansion  by  a  slight  turning 
of  the  screwed  joint,  the  turning  being  so  small  that  the  joint 
does  not  leak  even  after  being  used  a  number  of  years.  When 
made  as  shown  in  Fig.  115  this  expansion  joint  does  not  inter- 
fere with  the  flow  of  condensation. 

178.  Erecting  Pipe. — The  constructive  details  of  steam 
piping  have  been  so  well  worked  out  that  only  a  few  of  the  most 
important  points  need  be  touched  upon.  The  defects  usually 
noted  are  poor  alignment  of  the  piping,  inadequate  provision  for 
expansion  and  drainage,  and  improper  placing  of  valves. 

If  the  piping  is  not  in  proper  alignment,  excessive  strains  are 


226 


STEAM  BOILERS 


thrown  on  the  flanges.  As  a  rule,  this  is  brought  about  by 
the  flanges  having  been  forced  into  contact  with  each  other  by 
tightening  on  the  joining  bolts  instead  of  placing  the  pipe  so 
the  flanges  will  fit  together.  The  flanges  of  modern  steel  pipe 
are  amply  strong  if  they  are  fitted  together  properly  but  if  they 
are  not  lined  up  properly  very  heavy  strain  will  be  brought  upon 
them.  If  the  flanges  do  not  come  close  enough  together,  a  thin 
ring  of  metal  should  be  put  in  to  make  up  the  length.  When 
erecting  heavy  pipes,  every  length  should  be  placed  in  position 


FIG.  116. 

and  properly  supported  and  leveled  by  its  own  slings  and  brackets, 
and  the  flanges  should  not  be  bolted  together  permanently  until 
this  is  done. 

A  good  method  of  connecting  engines  to  boilers,  allowing 
ample  provision  for  expansion  and  drainage,  is  shown  in  Fig. 
116.  By  the  use  of  bends  of  large  radius,  provision  for  expan- 
sion is  made  with  but  few  fittings,  and  the  piping  has  sufficient 
slope  for  drainage.  A  good  rule  to  follow  in  determining  which 
way  the  piping  should  slope  is  to  arrange  the  stop  valve  of  the 
boiler  so  that  all  condensation  between  it  and  the  boiler  will 
drain  back  into  the  boiler,  and  to  slope  the  piping  beyond  the 


PIPING  AND  BOILER  FITTINGS 


227 


valve  so  that  water  will  drain  away  from  the  boiler  toward  the 
engine.  If  several  boilers  are  connected  to  a  header,  the  con- 
densation between  the  stop  valve  and  the  header  may  be  drained 
into  the  header  and  the  header  drained  by  means  of  a  bleeder 
pipe. 

The  position  and  method  of  placing  valves  is  a  very  important 
matter  and  one  which  does  not  always  receive  the  attention 
which  it  should.  In  placing  stop  valves  the  first  and  most 
important  feature  is  to  ascertain  whether  the  valve  will  act  as  a 
water  trap  for  condensed  steam.  Fig.  117  illustrates  a  common 
error  in  the  placing  of  valves  as  this  arrangement  permits  an 


FIG.  117.— Wrong  method. 


FIG.  118.— Right  method. 


accumulation  of  condensed  steam  above  the  valve  when  closed, 
and  should  the  engineer  open  the  valve  suddenly,  serious  results 
would  follow,  owing  to  water-hammer.  Fig.  118  illustrates  the 
correct  method  of  placing  the  valve.  It  sometimes  happens, 
however,  that  it  is  not  convenient  to  place  the  valve  as  shown  in 
Fig.  118  and  that  the  other  position  is  the  only  place  in  which 
the  valve  can  be  inserted.  In  such  cases  the  valve  should  have 
a  drain  and  this  drain  should  always  be  opened  before  the  large 
valve  is  opened. 

Lead  or  pipe  grease  used  in  erecting  piping  should  be  put  on  the 
pipe  thread  rather  than  on  the  valve  thread.     When  the  steam 
is  turned  on,  this  stuff  is  carried  to  the  bearing  parts   of  the 
20 


228  STEAM  BOILERS 

valve,  and,  owing  to  its  sticky  nature,  catches  and  holds  grit 
and  scale  on  the  seats  and  discs  of  the  valve,  where  it  causes 
cutting. 

In  screwing  a  valve  on  a  pipe,  the  mistake  is  often  made  of 
placing  the  wrench  on  the  hexagon  furthest  from  the  end  of  the 
pipe.  This  brings  a  great  twisting  strain  upon  the  body  of  the 
valve  placing  the  seat  out  of  line  and  causing  the  valve  to  leak. 

Piping  should  be  cleaned  out  before  being  placed  in  position 
and,  if  possible,  the  line  should  be  blown  out  after  the  valves  are 
in  place.  Unless  this  is  done,  loose  scale  and  metal  chips 
remaining  in  the  pipe  may  injure  the  valve  seats  or  discs,  causing 
leaks.  Should  a  valve  leak  slightly,  considerable  damage  often 
results  by  applying  additional  leverage  to  the  hand  wheel  to  ob- 
tain a  tight  joint.  The  valve  should  be  reground  as  soon  as 
possible  to  secure  a  tight  joint. 

In  putting  together  screwed  joints,  pipe  fitters  often  make  a 
mistake  in  putting  the  white  lead,  oil,  or  other  cementing 
material  on  the  inside  thread  or  female  fitting.  This  should  not 
be  done,  as  when  the  fitting  is  screwed  up,  the  end  of  the  pipe  or 
threads  will  often  carry  the  cementing  material  along  in  front  of  it 
and  this  will  collect  inside  the  female  fitting  and  cause  a  stricture 
or  reduction  of  area.  The  cementing  paste  should,  therefore, 
always  be  put  on  the  outside  or  male  thread.  This  will  ac- 
complish the  same  purpose  and  give  better  results. 
«  179.  Pipe  Covering. — When  saturated  steam  is  conveyed 
through  pipes  a  portion  of  it  will  condense,  the  amount  depending 
upon  the  temperature  of  the  steam  and  the  velocity  and  tem- 
perature of  the  air  surrounding  the  pipe.  This  condensation 
causes  a  loss  not  only  of  volume  of  steam,  but  of  efficiency  in 
utilizing  the  remainder  of  the  steam  when  it  reaches  the  engine. 
Consequently,  where  fuel  economy  is  an  object,  all  steam  pipe, 
boiler  steam  drums,  receivers,  etc.,  should  be  covered  with  some 
efficient  heat  insulating  material,  and  the  saving  thus  effected 
will  pay  large  interest  on  the  investment. 

It  has  been  experimentally  determined  that  each  square 
foot  of  bare  iron  pipe  surface  will  radiate  about  3  B.t.u.  per  hour 
for  each  degree  Fahrenheit  difference  between  the  temperature  of 
the  steam  in  the  pipe  and  the  air  surrounding  it,  the  exact  amount 
varying  with  the  velocity  of  the  air  and  the  moisture  in  it.  For 
practical  purposes  3  B.t.u.  per  hour  may  be  assumed.  To 
determine  the  money  value  of  the  loss  in  any  particular  case, 


PIPING  AND  BOILER  FITTINGS  229 

determine  the  square  feet  cf  exposed  pipe  surface,  and  the  tem- 
perature of  the  steam  by  reference  to  a  steam  table;  assume  the 
temperature  of  the  air  surrounding  the  pipe  and  then  compute 
the  temperature  difference.  Conditions  of  operation  of  the  plant 
will  approximately  determine  the  number  of  hours  each  year 
during  which  steam  will  be  in  the  pipe  line,  hence,  the  total 
B.t.u/s  lost  per  year  can  be  roughly  determined.  This,  divided 
by  965.8  will  give  the  number  of  pounds  of  steam  from  and  at 
212°  equivalent  to  this  loss;  the  evaporation  per  pound  of  coal 
and  the  cost  of  coal  per  ton  (including  cost  of  handling  it  and  the 
ashes)  being  known,  the  money  value  of  the  loss  is  at  once 
determined. 
This  may  be  put  into  a  formula  as  follows  : 

-    .  , 

Cost  per  year  of  steam  condensed  = 


965.8xJgx20o 

in  which  A   =  area  of  exposed  pipe  surface  in  square  feet 

t  =  temperature  of  steam 

ti  =  average  temperature  of  surrounding  air 
N  =  hours  per  year  steam  is  in  pipe 
E  =  evaporation  from  and  at  212°  per  pound  of  coal 
C  =  cost  of  coal  and  handling  per  ton. 

The  application  of  this  formula  may  be  illustrated  by  the 
following  example.  In  a  certain  power  plant  there  is  a  line  of 
bare  pipe  made  up  of  150  ft.  of  3-in.  and  50  ft.  of  2-in.  pipe 
carrying  a  pressure  of  135  Ib.  per  sq.  in.  absolute  and  with 
air  at  90°  temperature  surrounding  the  pipe.  The  cost  of  coal, 
including  handling  is  $3.20  per  ton  and  7  Ib.  of  water  are  evapo- 
rated from  and  at  212°  per  pound  of  coal.  What  will  be  the 
loss  from  the  steam  pipe  when  the  plant  runs  24  hours  a  day  for 
360  days  in  the  year? 

Referring  to  the  table  of  pipe  sizes  we  see  that  it  takes  1.091 
lineal  feet  of  3-in.  pipe  and  1.611  lineal  feet  of  2-in.  pipe  to  have 
1  sq.  ft.  of  external  surface.  The  external  area  of  the  3-in.  pipe 

will  therefore  be  3-^^  =  137.3  sq.  ft.  and  of  the  2-in.  pipe 


1 
i.  oil 

=  31  sq.  ft.  The  total  external  area  of  bare  pipe  is  therefore 
137.3+31  =  168.3  sq.  ft.  The  temperature  of  the  steam  is,  from 
the  steam  table,  350°  and  the  number  of  hours  per  year  which  the 
plant  runs  is  360X24  =  8640,  therefore,  the  cost  of  the  steam 
condensed  in  the  bare  pipe  is 


230  STEAM  BOILERS 


965.8  X#X  2000 

^3X168.3X  (350-90)  X  8640X3.20 
965.8X7X2000 

=  $268.43  per  year. 

By  properly  applying  a  covering  of  good  grade,  as  much  as 

90  per  cent  of  the  loss  from  condensation  may  be  saved.     There 

are  many  brands  of  coverings  on  the  market  and  the  only  practical 

way  to  be  sure  of  what  each  will  do  is  either  to  purchase  of  a  firm 

v  of  established  integrity  or  else  make  comparative  tests. 

There  is  a  dearth  of  accurate  data  on  the  life  of  pipe  covering  of 
different  kinds.  It  is  well  known,  however,  that  as  a  result  of 
constant  vibration  some  of  them,  when  on  horizontal  pipe  lines, 
lose  their  shape,  hang  loose  on  the  pipe  and  allow  the  material  to 
shift  so  that  the  covering  becomes  thicker  on  the  bottom  than  on 
the  top.  Only  previous  experience  or  careful  inquiry  as  to  the 
experience  of  others  can  indicate  what  defects  of  this  nature  may 
develop  in  a  covering  after  it  has  long  been  in  use. 

Pipe  covering  may  be  either  sectional,  that  is,  molded  to  shape 
and  attached  to  pipes  by  bands,  etc.,  so  it  can  be  removed  at  any 
time;  or  plastic,  which  is  mixed  in  the  shape  of  a  mortar,  and 
built  up  on  the  pipe  in  layers,  so  that  it  cannot  be  removed  and 
replaced  without  working  it  over.  The  former  has  more  joints, 
and  often,  under  vibration,  changes  shape,  but  it  is  more  con- 
venient for  work  subject  to  future  alterations.  The  plastic 
covering  obviates  joints,  adheres  closely  to  the  pipe  if  of  proper 
quality  and  workmanship,  needs  few  repairs  and  the  thickness 
can  be  varied  to  suit.  It  is  more  difficult  to  apply  than  sectional 
covering,  but  more  permanent  when  applied. 

Pipe  .  coverings  should  receive  the  same  care  and  frequent 
inspection  as  other  parts  of  the  plant.  Their  efficiency  quickly 
falls  off  if  air  is  allowed  to  circulate  between  them  and  the  pipe 
and,  if  allowed  to  become  wet,  they  only  increase  the  evil  they 
are  expected  to  remedy. 

The  following  table  gives  some  idea  of  the  insulating  qualities 
of  a  few  of  the  more  common  kinds  of  pipe  coverings.  In  the 
last  column  will  be  found  the  number  of  heat  units  lost  per  square 
foot  of  pipe  surface  per  hour  for  each  degree  difference  in  tem- 
perature between  the  steam  and  the  air  surrounding  the  pipe. 


PIPING  AND  BOILER  FITTINGS 

BARRUS'  TESTS  OF  PIPE  COVERINGS 


231 


Cost 

Diff.  of 

X-T     4- 

AT^4- 

B.t.u  lost 

Name  of  covering 

(applied) 
per 
running 
foot, 

temp, 
between 
steam 
and  air, 

jNet 
surface 
of  bare 
pipe, 
sq.  ft. 

JNet 
conden- 
sation 
per  hour, 
Ib. 

per  square 
foot  per 
hour  per  de- 
gree diff  .  in 

cents 

deg.  F. 

temp. 

80-lb.  Pressure,  2-in.  Pipe 

Asbestocell  

13.60 

263.0 

63.68 

13.47 

.728 

New  York  air  cell  

16.32 

256.6 

63.24 

13.43 

.750 

Carey's  molded   

12.64 

261.9 

64.12 

14.23 

.768 

Asbesto-sponge  molded  

12.64 

261.9 

63.84 

14.35 

.778 

Gast's  air  cell  

14.56 

262.6 

63.64 

14.63 

.793 

150-lb.  Pressure,  2-in.  Pipe 

A-S  hair-felt,  3-ply  plain  

23.89 

303.5 

64.41 

10.22 

.462 

A-S  hair-felt,  2-ply  corrugated.  . 

20.11 

304.9 

64.21 

10.86 

.490 

A-S  felt,  59  laminations  

23.20 

304.1 

63.78 

10.76 

.490 

A-S  felt,  48  laminations  

23.20 

294.0 

64.21 

11.35 

.531 

Magnesia                  .... 

25.12 

300.6 

63.66 

11.50 

.531 

Asbestos,  navy  brand  

22.24 

300.6 

63.82 

13.16 

.606 

150-lb.  Pressure,  10-in.  Pipe 

A-S  felt,  76  laminations  

78.30 

302.0 

97.10 

9.29 

.280 

A-S  felt,  66  laminations  

59.00 

315.0 

97.10 

10.60 

.306 

Magnesia  

71.00 

299.2 

97.10 

11.64 

.354 

Asbestos,  navy  brand  

67.70 

298.4 

97.81 

12.79 

.387 

Watson's  imperial,  1  in  

41.00 

303.0 

97.81 

14.37 

.428 

Bare  Pipes 

2-in  pipes  80-lb  pressure 

273.2 

63.70 

59.16 

3.081 

2-in  pipes   150-lb   pressure 

305.2 

63.98 

74.40 

3.366 

10-in  pipes  150-lb  pressure 

295.4 

100.45 

107.84 

3.220 

The  saving  to  be  derived  from  covering  pipes  may  be  calcu- 
lated from  the  preceding  formula.  For  example,  suppose  the 
pipe  mentioned  in  the  example  just  given  had  been  covered  with 
asbesto-sponge,  of  which  the  factor  of  heat  loss  is  0.778,  the 
cost  of  the  steam  condensed  in  the  pipes  would  be 


.778  X  168  3  X  (350-90)  X  8640X  3.20 
968.5X7X2000 


=  $69.42 


Comparing  this  with  the  $268.40  lost  per  year  with  the  bare  pipe, 
it  will  be  seen  that,  by  covering  the  pipe,  a  saving  of  $268.40  — 
69.41  =$198.99  per  year  will  be  effected. 

180.  Boiler  Fittings. — The  fittings  usually  supplied  with  a  new 
boiler  are  safety  valves,  steam  gages,  water  gages,  safety  plugs 
and  blow-off  valve  and  connections,  and  sometimes  also  a  water 
column  and  surface  blow-off. 


232 


STEAM  BOILERS 


181.  Safety  Valves. — There  are  two  general  types  of  safety 
valves  in  common  use,  viz.,  the  lever  safety  valve  and  the  pop 
safety  valve. 

Tl>e  lever  safety  valve  is  shown  in  Fig.  119.  This  valve  con- 
sists of  an  iron  or  brass  body  shaped  very  much  like  an  angle 
globe  valve,  and  having  on  the  inside  an  opening  closed  by  a  disc 
ground  to  fit  tightly  on  a  seat.  From  the  disc,  a  spindle  or  stem 
extends  out  through  the  top  of  the  valve  body,  the  stem  passing 
through  a  stuffing  box  which  serves  to  prevent  steam  from  leak- 
ing past  and  also  to  guide  the  disc  so  it  will  seat  itself  properly. 
The  disc  is  held  on  its  seat  by  means  of  a  lever  and  weight.  The 
lever  is  pivoted  at  one  end  to. the  valve  case,  and  rests  upon  the 


70         So" 


FIG.  119. — Lever  safety  valve. 

end  of  the  stem  as  shown,  the  weight  serving  to  hold  it  down 
against  the  pressure  on  the  under  side  of  the  disc  which  is  tending 
to  raise  it.  The  lever  is  marked  at  a  number  of  points  with  a 
number  which  indicates  the  pressure  in  the  boiler  which  will 
open  the  valve  when  the  weight  is  placed  at  that  particular 
point.  Thus  the  arrangement  forms  an  adjustable  safety  valve 
which  will  open  automatically  when  the  pressure  reaches  a  cer- 
tain predetermined  amount. 

The  point  at  which  the  weight  should  be  placed  in  order  for 
the  valve  to  open  under  any  desired  pressure  may  be  found  as 
follows : 

Let   a  —  area  of  opening  in  valve  seat  in  square  inches 

1  =  distance  in  inches  of  pivot  point  from  point  where 

stem  touches  lever 

P  —  pressure  in  boiler  in  pounds  per  square  inch 
W  —  Weight  of  ball  in  pounds 
w  =  Weight  of  lever  in  pounds 


PIPING  AND  BOILER  FITTINGS  233 

L  =  Distance  in  inches  at  which  ball  is  placed  from  the 

pivot  point 
X  =  total  length  in  inches  of  lever  bar. 


WXL+WX^ 
and  P«- 


This  equation  will  give  the  pressure  at  which  the  valve  will 
open  for  any  given  position  of  the  weight,  and  the  equation 


L 


will  give  the  distance  which  the  ball  must  be  placed  from  the 
pivot  point  in  order  to  open  at  any  given  pressure. 

Example  :  Where  should  the  weight  be  placed  on  a  lever  safety 
valve  which  has  a  disc  opening  of  3-in.  diameter,  if  the  ball 
weighs  140  lb.,  the  lever  is  30  in.  long  and  weighs  3  lb.,  the  pivot 
point  is  4  in.  from  the  point  at  which  the  stem  touches  the  lever, 
and  the  pressure  at  which  it  is  desired  that  the  boiler  blow-off 
is  130  lb.  per  sq.  in.? 

Solution: 

L 


T 


,_7xl30x4-45 

~ 


=  25.7  in.  from  pivot. 

The  lever  safety  valve  is  one  of  the  oldest  types  to  be  used, 
and  has  the  advantage  of  being  simple  in  construction  and 
reliable  in  action  but  it  is  easily  tampered  with  and,  as  this  is  a 
dangerous  feature,  it  has  caused  this  type  of  safety  valve  to  fall 
into  disuse  for  high-pressure  boilers. 

A  common  form  of  pop  safety  valve  is  shown  in  Fig.   120. 


234 


STEAM  BOILERS 


In  the  pop  safety  valve  the  disc  is  held  firmly  on  its  seat  by  the 
pressure  of  a  stiff  coil  spring  which  may  be  adjusted  to  exert  a 
greater  or  less  pressure  on  the  disc  in  order  to  make  it  open  under 
a  greater  or  less  pressure.  The  greatest  objection  to  these  valves 
is  that,  when  they  are  on  the  point  of  opening,  they  simmer  or 
vibrate  rapidly  and  make  a  very  disagreeable  humming  noise. 
This  may,  however,  be  overcome  to  a  great  extent  by  placing 
on  the  valve  a  muffler,  which  consists  of  a  number  of  perforated 


FIG.  120. — Pop  safety  valve. 

plates  for  breaking  up  the  streams  of  steam  escaping  from  the 
valve. 

Pop  safety  valves  are  adjusted  by  tightening  or  loosening  the 
spring  pressure  on  the  valve  disc.  Some  valves  are  provided 
with  means  for  sealing  or  locking  the  case,  in  order  to  prevent 
them  from  being  tampered  with  after  they  are  once  adjusted. 
The  one  shown  in  the  figure  above  is  of  this  type. 

Pop  safety  valves  are  made  in  sizes  up  to  6-in.  diameter;  if  a 
larger  size  than  this  is  needed  it  is  necessary  to  use  two  valves. 
In  any  case  it  is  better  to  have  two  safety  valves  on  a  boiler,  in 
order  that  if  one  should  not  be  in  working  order,  the  other 


PIPING  AND  BOILER  FITTINGS  235 

may  operate.  Nearly  all  safety  valves  have  seats  beveled  off  at 
an  angle  of  45  degrees,  and  the  seats  of  the  better  grades  are  made 
of  nickel  to  prevent  corrosion.  Pop  valves  are  usually  made  to 
close  when  the  pressure  has  dropped  about  5  Ib.  below  its  opening 
pressure.  This  is  done  by  making  an  extension  on  the  valve  so 
that  when  it  is  open  it  will  present  more  area  to  the  steam 
pressure  than  when  closed. 

Various  rules  of  more  or  less  merit  have  been  proposed  for 
finding  the  size  of  pop  safety  valve  that  should  be  placed  on  a 
boiler  of  given  size,  but  the  one  given  below  is  believed  to  be  the 
best.  This  formula,  which  is  based  upon  experiments  made  by 
Mr.  D.  G.  Darling  in  1908,  is  as  follows: 


in  which  D    is  the  diameter  of  the  valve  seat  in  inches,  which, 
in  most  valves,  is  approximately  the  same  as  the 
inlet  diameter  of  the  valve. 
W  is  the  maximum  number  of  pounds  of  waler  the 

boiler  will  evaporate  per  hour 
L    is  the  lift  of  the  valve  in  inches 
and  P    is  the  absolute  pressure  carried  by  the  boiler  in 

pounds  per  square  inch. 

This  formula  may  be  simplified  and  made  to  suit  ordinary 
conditions  by  asuming  a  factor  of  evaporation  of  1.1,  a  lift  of 
the  valve  of  .11  in.  and  assuming  also  that  the  boiler  has  a 
maximum  capacity  equal  to  twice  its  rated  horse-power.  The 
formula  then  becomes 


in  which  D  and  P  have  the  same  meaning  as  before  and  h.p.  is 
the  nominal  horse-power  rating  of  the  boiler. 

Example  :  What  size  pop  safety  valve  should  be  placed  on  a 
300  h.p.  boiler  which  carries  125  Ib.  steam  pressure? 

D  =  5.42X^^  =  81  in.  (approximately). 
LZo 

This  boiler  could  be  supplied  with  one  4-in.  and  one  5-in. 
valve.  The  diameter  as  given  by  the  formula  is  the  combined 
diameter  of  all  the  valves  on  the  boiler,  the  combined  diameter 
being  the  sum  of  the  diameters  of  the  separate  valves. 


236 


STEAM  BOILERS 


A  safety  valve  should  not  be  tested  by  opening  it  by  hand, 
but  to  insure  its  being  in  proper  working  order,  the  steam  pres- 
sure should  be  raised  until  the  valve  begins  to  simmer  and  the 
pressure  indicated  on  the  gage  noted.  The  pressure  should  then 
be  further  raised  until  the  valve  opens.  The  safety  valve  should 
be  tested  in  this  way  at  least  once  each  day  to  insure  its  satis- 
factory action. 

182.  Steam  Gages. — The  ordinary  form  of  a  steam  gage,  often 
called  a  Bourdon  gage,  consists  of  a  circular  spring  passing  around 
the  inside  of  the  case,  and  this  spring  is  attached  by  a  series  of 


FIG.  121. — Steam  gage  mechanism. 

levers  to  a  train  of  gears  which  move  the  needle.  See  Fig.  121. 
The  cross-section  of  the  spring  is  in  the  form  of  an  oval  made  by 
flattening  a  round  tube.  Any  pressure  applied  to  the  inside  of 
this  tubular  spring  tends  to  make  it  assume  a  circular  cross- 
section,  but  before  it  can  do  so,  it  must  be  straightened  out. 
Since  the  spring  is  fastened  rigidly  at  one  end,  while  the  other 
end,  which  is  attached  to  the  levers,  is  free  to  move,  any  pressure 
applied  to  the  inside  of  it  causes  the  free  end  to  move  and  thus 
imparts  motion  to  the  levers  and  to  the  hand  which  moves  over 
a  graduated  dial.  A  vacuum  gage  is  made  in  the  same  way, 


PIPING  AND  BOILER  FITTINGS  237 

except  that  the  levers  are  pivoted  in  such  a  manner  as  to  cause 
the  hand  to  move  in  the  opposite  direction  to  what  it  would  in  a 
pressure  gage. 

One  end  of  the  spring  in  a  steam  gage  is  soldered  directly  to 
the  case  on  the  inside,  while  the  pipe  connection  is  fastened  to  the 
outside.  At  high  pressures  the  temperature  of  steam  is  suffi- 
cient to  melt  a  soldered  joint  and  for  this  reason  it  is  necessary  to 
prevent  the  steam  from  coming  in  direct  contact  with  the  joint. 
This  is  done  by  connecting  the  gage  to  a  loop  of  pipe  which  has 
water  in  it.  When  steam  is  admitted  to  the  pipe,  its  pressure  is 
exerted  upon  the  water  and  the  spring  is  then  filled  with  water 
instead  of  steam. 

Another  class  of  gages,  though  not  a  very  common  one,  is 
known  as  the  diaphragm  gage.  In  this  gage  the  needle  is  moved 
by  the  vertical  movement  of  a  pin,  the  lower  end  of  which 
rests  on  one  side  of  a  diaphragm  while  steam  presses  on  the 
other  side  of  it.  The  pressure  of  the  steam  causes  the  diaphragm, 
which  is  made  of  a  thin  sheet  of  corrugated  metal,  to  be  deflected 
upward  and  this  motion  is  imparted  to  the  pin  which  rests 
upon  it. 

183.  Water  Gages. — Water  gages  are  for  the  purpose  of  indi- 
cating to  the  observer  the  height  of  the  water  level  in  the  boiler. 
They  consist  of  one  connection  above  the  water  line  and  one 
below,  fitted  with  valves  and  having  a  strong  glass  tube  between 
the  connections  as  shown  in  Fig.  122.  If  both  gage  cocks  are 
open,  the  water  will  stand  at  the  same  height  in  the  glass  tube 
that  it  does  in  the  boiler,  and  this  forms  a  very  ready  means  of 
noting  the  water  level.  Water  gages  are  usually  about  12  in. 
long,  set  so  the  middle  of  the  tube  is  at  about  the  ordinary  water 
level.  As  any  discoloring  matter  in  the  water  will  stain  the 
glass  tube  and  make  it  difficult  to  see  the  water  level,  water  gages 
are  usually  supplied  with  a  drain  cock  at  the  bottom  through 
which  they  may  be  blown  out.  In  order  to  blow  out  the  glass 
it  is  only  necessary  to  close  the  bottom  connection  to  the  boiler 
and  open  the  blow-out  cock,  when  steam  will  enter  from  the  top 
and  will  blow  through  the  tube.  Sometimes  the  tube  will  become 
so  badly  stained  that  steam  will  not  clean  it,  when  it  becomes 
necessary  to  clean  the  glass  with  hydrochloric  or  muriatic  acid. 
The  water  gage  should  be  blown  out  at  least  once  a  day  and 
preferably  oftener,  to  make  sure  that  it  is  in  proper  working 
order;  but  after  this  is  done  one  must  be  very  careful  to  see  that 


238 


STEAM  BOILERS 


both  cocks  are  open,  else  the  gage  will  not  indicate  correctly. 
If  the  top  cock  is  closed  and  the  bottom  one  open,  the  pressure  on 
the  inside  of  the  boiler  will  force  the  water  too  high  in  the  glass. 
If  the  bottom  cock  is  open  and  the  top  one  closed,  the  steam 
entering  the  top  will  gradually  condense  and  fill  the  tube  with 
water,  showing  a  higher  water  level  than  that  actually  in  the 
boiler.  If  both  cocks  are  closed,  the  gage  will  of  course  not 
indicate  changes  in  the  water  level,  and  high  or  low  water  may 
result  without  the  fireman  knowing  it.  Fig.  123  shows  the 
details  of  the  packing  at  one  end  of  a  gage  glass. 


FIG.  122. 


FIG.  123. 


On  account  of  both  the  water  and  the  gage  glass  being  colorless, 
it  is  sometimes  difficult  to  see  the  height  of  the  water  in  an 
ordinary  gage.  To  overcome  this  difficulty  a  type  of  water  gage 
shown  in  Fig.  124  has  been  designed  in  which  the  water  in  the 
gage  shows  black  and  the  steam  shows  white.  This  result  is 
secured  by  placing  in  front  of  the  gage  glass  a  plate  of  thick  glass 
having  facets  cut  in  the  back.  These  gages  represent  a  decided 
improvement  over  the  old  form,  making  the  water  level  easily 
seen. 

Great  care  should  be  taken  to  prevent  live  steam  or  hot  water 
from  coming  in  contact  with  a  cold  gage  glass,  as  the  sudden 
expansion  is  likely  to  cause  the  glass  to  explode,  sometimes 
causing  serious  injury  to  those  standing  nearby.  When  a  gage 
glass  becomes  broken,  it  is  a  very  disagreeable  task  to  shut  off 
the  steam  and  hot  water  which  is  escaping  through  the  cocks  at 
the  top  and  bottom.  To  obviate  the  nuisance  of  having  to  close 


PIPING  AND  BOILER  FITTINGS 


239 


gage  cocks  while  steam  is  escaping,  some  gages  are  fitted  with 
automatic  valves  at  the  top  and  bottom  so  that  when  the  glass 
breaks,  the  valves  close  automatically  and  shut  off  the  steam 
and  water.  Although  these  cost  more,  it  is  better  to  use  them. 

184.  Gage  Cocks. — From  what  has  been 
said  above,  it  can  be  seen  that  a  water 
gage  cannot  be  absolutely  depended  upon, 
and  therefore   some  other  means  should 
be  provided  for  indicating  the  height  of 
the  water  level.     This  is  usually  done  by 
providing    three-hand     operated    valves 
which    open    directly    into    the    boiler. 
These  valves  are  called  Gage  Cocks.     The 
lower  one    is  usually  placed  3  in.  above 
the  top  row  of  tubes  in  a  fire-tube  boiler, 
the  second   being  3  or  3J  in.  above  the 
first,  and  the  third  3  or  3J  in.  above  the 
second.     The  water  should  be  kept  be- 
tween the  second  and  third  cocks.     Upon 
opening  one  of  these  cocks,  if  water  comes 
out  the  water  level  is  above  the  cock,  but 
if  a  mixture  of  water  and  steam  comes  out, 
the  cock  is  just  on  the  water  line.     The 
glass  gage  should  not  be  depended  upon 
entirely,  but  the   gage   cocks   should  be 
tried  frequently  to  see  that  the  gage  is 
indicating  correctly. 

185.  Water  Columns. — The  steam  gage, 
water  gage,  and  gage  cocks  are  sometimes 
combined  into  one  device  called  a  water 
column.     Such  a  device  is  shown  in  Fig. 
125.     It  consists  of  a  hollow  cast-iron  ves- 
sel connected  at  the  top  with  the  steam 
space  and  at  the  bottom  with  the  water 
space  of  the  boiler.     The  steam  gage  is 

mounted  upon  the  top  of  the  column,  the  gage  glass  on  one 
side  and  the  gage  cocks  on  the  other.  Sometimes,  as  shown 
in  Fig.  125,  there  is  placed  on  the  water  column  a  small  whistle 
which  is  blown  if  the  water  becomes  too  low  or  too  high,  thus 
giving  audible  warning  of  these  dangerous  conditions.  The 
whistle  is  usually  operated  by  means  of  a  float  which  will  open 


FIG.  124. 


240 


STEAM  BOILERS 


the  valve  leading  to  it  if  the  float  reaches  a  predetermined  upper 
or  lower  limit.  A  serious  objection  to  such  devices  as  this  is 
that  they  tend  to  make  the  fireman  careless.  The  fireman  will 
come  to  depend  on  the  automatic  action  of  the  water  column  to 
tell  him  when  more  water  is  needed  and  he  does  not  watch  the 
gage  glass  closely  enough,  with  the  result  that  sometimes  the 
alarm  will  fail  to  operate,  the  water  will  become  too  low,  and  the 
boiler  be  injured  or  an  explosion  occur. 

186.  Safety  Plugs.— This  is  another  de- 
vice for  protecting  a  boiler  from  injury 
in  case  of  low  water.  It  consists  of  a 
brass  or  bronze  plug  which  may  be  screwed 
into  the  shell  of  the  boiler,  the  plug  being 
bored  out  and  filled  with  pure  tin  or  some 
composition  metal  which  has  a  melting- 
point  but  little  above  the  temperature  of 
the  steam  in  the  boiler.  Fig.  126  shows 
one  type  of  safety  plug. 

Safety  plugs  are  placed  in  the  rear  or 
front  heads,  just  a  little  above  the  top 
row  of  tubes  in  return  fire-tube  boilers  and 
usually  in  the  crown-sheet  just  over  the 
grate  in  a  locomotive  type  of  boiler.  The 
metal  of  the  plug  transmits  the  heat  to  the 
water  so  rapidly  that  its  temperature  does 
not  rise  if  it  is  covered  with  water,  but, 
if  the  water  level  sinks  below  the  plug, 
the  plug  will  become  heated  sufficiently 
to  melt  the  soft  metal  core  and  allow 

steam  to  escape  through  it  and  give  warning  of  the  dangerous 
condition  of  the  water  level. 

As  soot  will  collect  on  the  fire  side  of  the  plug  and  scale  on  the 
water  side  and  both  of  these  may  prevent  the  plug  from  operating 
when  needed,  it  is  necessary  to  scrape  them  both  outside  and 
inside  occasionally  in  order  to  keep  them  in  good  working  con- 
dition. At  the  best,  safety  plugs  are  unreliable,  but  some  states 
require  them  by  law. 

187.  Surface  and  Bottom  Blow-offs. — The  surface  blow-off  is 
for  the  purpose  of  blowing  off  scum,  foam,  and  floating  matter 
from  the  surface  of  the  water  in  the  boiler,  and  to  relieve  exces- 
sive priming.  It  consists  usually  of  a  funnel  placed  near  the 


FIG.  125. 


PIPING  AND  BOILER  FITTINGS  241 

rear  head  of  the  boiler  and  having  its  center  about  on  the  usual 
water  level  as  in  Fig.  127.  The  funnel  connects  with  a  pipe 
leading  to  the  outside  and  provided  with  a  valve.  The  end  of 
the  pipe  inside  the  boiler  is  provided  with  a  funnel  in  order  to 
insure  draining  the  scum  when  the  water  is  at  different  levels. 


FIG.  126. — Safety  plug. 

The  proper  way  to  operate  a  surface  blow-off  is  to  open  it  for  a 
few  seconds  about  every  15  minutes  or  longer  as  required,  rather 
than  to  open  it  for  a  longer  period  at  longer  intervals. 

The  bottom  blow-off  consists  simply  of  a  pipe  opening  into 
the  boiler  at  its  lowest  point  and  provided  with  the  proper 


FIG.  127. — Surface  blow-off. 

valves.  The  boiler  should  be  set  so  that  the  point  of  most 
sluggish  circulation  is  also  the  lowest  point,  as  the  mud  and 
sediment  will  be  likely  to  settle  at  a  point  where  the  circulation 
is  slowest.  On  a  fire-tube  boiler  the  bottom  blow-off  is  usually 
placed  at  the  back  end  which  is  a  little  lower  than  the  front  end. 


242  STEAM  BOILERS 

On  a  water-tube  boiler  it  is  usually  attached  to  a  mud  drum, 
which  is  arranged  to  catch  the  mud  and  sediment  and  which  is 
generally  placed  at  the  lowest  point  of  the  boiler. 

Blow-off  valves  will  probably  give  more  trouble  than  any  other 
boiler  fitting  owing  to  the  wearing  and  corroding  action  of  the 
dirty  water  passing  through  them  and  to  their  liability  to  clog 
up.  Ordinarily,  an  angle  valve  should  be  used  where  possible,  as 
this  offers  a  freer  passage  for  the  water  and  the  valve  is  more 
likely  to  seat  properly. 

A  very  satisfactory  valve  for  this  purpose  is  made  like  a  water 
cock  but  packed  with  asbestos  to  prevent  leakage.  This  is 
simpler  and  less  liable  to  get  out  of  order  than  most  forms  of 
valves.  The  blow-off  pipe  should  be  provided  with  two  valves, 
the  one  nearest  the  boiler  being  a  special  blow-off  valve,  and  the 
other  may  be  an  ordinary  gate  valve.  As  the  hot  water  passing 
through  a  blow-off  pipe  will  disintegrate  tile  sewer  pipe,  the 
blow-off  should  never  enter  a  sewer  made  from  tile  pipe  until  the 
water  has  been  cooled  somewhat.  A  very  good  arrangement  is 
to  blow  the  boilers  off  into  a  special  iron  tank  provided  with  a 
coil  of  pipe  through  which  the  feed  water  flows  on  its  way  to  the 
feed-water  heater  or  the  boiler.  By  this  arrangement  a  part  of 
the  heat  that  would  otherwise  be  lost  is  saved.  After  the  blow- 
off  water  is  cooled  by  the  feed  water  it  may  be  allowed  to  flow 
into  the  sewer. 

Blow-off  pipes  are  often  run  under  floors  or  other  out-of-the- 
way  places  where  they  cannot  be  readily  seen.  This  should  not 
be  done,  as  a  leak  will  not  be  detected  and  a  leak  in  the  blow-off 
valve  is  a  dangerous  thing,  causing  low  water  quickly,  besides 
wasting  a  great  deal  of  heat.  If  it  is  necessary  to  run  a  blow-off 
pipe  where  it  cannot  be  readily  seen,  a  tell-tale  should  be  at- 
tached to  it.  A  tell-tale  may  be  constructed  by  placing  a  tee 
in  the  blow-off  pipe,  with  one  opening  pointing  downward. 
A  3/4-in.  pipe  provided  with  a  valve  is  attached  to  the  tee  and 
run  to  the  front  of  the  boiler  where  its  end  may  be  easily  seen. 
Then  if  a  leak  occurs,  the  water  will  pass  through  the  tee  and  tell- 
tale pipe  to  the  front  of  the  boiler  where  it  will  attract  attention. 
When  the  boiler  is  blown-off,  the  valve  on  the  tell-tale  pipe  must 
be  closed,  but  at  all  other  times  this  valve  is  left  open. 


CHAPTER  XV 
BOILER  ACCESSORIES 

188.  Dry  Pipes. — A  boiler  will  usually  form  wet  steam,  even 
when  working  at  its  rated  capacity  and,  if  it  is  forced,  the  steam 
may  contain  considerable  moisture  due  to  the  violent  bursting  of 
the  steam  bubbles,  which  throw  particles  of  water  into  the 
steam  space  when  they  remain  suspended  in  the  steam.  If  the 
boiler  is  forced  very  much  or  if  certain  impurities  exist  in  the 
feed  water,  priming  or  foaming  may  occur,  and  allow  large 
quantities  of  water  to  become  mixed  with  the  steam.  If  very 
wet  steam  is  allowed  to  enter  the  engine  cylinder,  the  water 
which  it  carries  is  liable  to  damage  the  engine.  A  further  ob- 
jection to  allowing  wet  steam  to  leave  the  boiler  is  that  wet  steam 
contains  less  energy  per  pound  than  dry  steam,  hence  a  larger 
amount  of  steam  must  be  handled  in  order  to  transfer  a  given 
amount  of  energy. 

A  device,  called  a  "dry  pipe,"  for  preventing  steam  from 
carrying  large  quantities  of  water  into  the  main  pipe  line  is 
supplied  with  most  boilers.  Nearly  all  dry  pipes  operate  on  the 
same  principle  as  the  separating  calorimeter;  that  is,  by  causing 
the  steam  to  make  a  sharp  turn  before  entering  the  main  pipe 
line,  thus  separating  the  water  from  the  steam  by  the  action  of 
centrifugal  force.  The  shape  of  the  dry  pipe  will  depend  largely 
upon  the  type  of  boiler  with  which  it  is  to  be  used,  since  some 
boilers  have  a  larger  steam  space  than  others,  and  can  therefore 
accommodate  a  larger  dry  pipe. 

One  of  the  simplest  forms  of  dry  pipe  is  shown  in  Fig.  128. 
This  dry  pipe  consists  of  a  tee  joined  to  the  end  of  the  main  steam 
outlet,  with  a  short  length  of  pipe  screwed  into  each  end.  These 
short  lengths  of  pipe  are  provided  with  caps  at  each  end  and 
have  a  series  of  small  holes  bored  near  the  top.  The  steam  being 
admitted  at  the  top,  is  taken  from  the  driest  portion  of  the 
steam  space,  and  on  entering  the  small  holes  a  large  part  of  the 
moisture  is  thrown  out  of  the  steam.  The  total  area  of  all  the 
holes  should  be  about  50  per  cent  greater  than  the  area  of  the 
outlet  in  order  to  prevent  a  loss  of  pressure  as  the  steam  enters 
21  243 


244 


STEAM  BOILERS 


the  dry  pipe.  In  addition  to  the  holes  in  the  top,  a  few  small 
holes  are  bored  in  the  bottom  near  each  end  for  draining  out  any 
water  that  may  enter  the  dry  pipe.  This  form  of  dry  pipe  gives 
excellent  results  and  is  especially  suited  to  those  boilers  which 
have  a  long  and  narrow  steam  space,  such  as  the  Babcock  and 
Wilcox  water-tube  boiler. 


FIG.  128. 


The  dry  pipe  is  frequently  made  in  the  form  of  a  trough  with 
the  top  of  the  boiler  shell  forming  a  covering  for  it.  The  edges 
of  the  trough  come  within  about  1/2  in.  ol  the  boiler  shell,  and 
the  steam  is  taken  over  the  edge  of  the  trough.  A  number  of 
small  holes  are  drilled  in  the  bottom  of  the  trough  for  draining 
the  water  from  it. 


FIG.  129. 

A  form  of  dry  pipe  which  does  not  require  much  space  is 
shown  in  Fig.  129.  It  consists  of  three  pans  placed  one  above 
the  other,  the  top  one  being  inverted  and  screwed  to  a  nipple 
which  enters  the  main  steam  outlet.  The  pans  are  held  at  a 
fixed  distance  apart  by  ferrules  which  surround  the  supporting 
bolts.  Steam  enters  over  the  edge  of  the  lower  pan  and  is  forced 
to  flow  downward  around  the  edge  of  the  upper  pan  before  it  can 
enter  the  main  steam  outlet,  thus  having  to  turn  through  an  angle 


BOILER  ACCESSORIES 


245 


of  180  degrees.  The  larger  part  of  the  moisture  is  thrown  into 
the  lower  pan,  from  which  it  is  drained  back  into  the  steam 
space  through  a  number  of  small  holes  in  the  bottom  of  this  pan. 
The  bottom  of  the  middle  pan  is  also  provided  with  a  number  of 
small  holes  for  draining  out  any  water  that  may  pass  the  lower 
pan. 

In  many  water-tube  boilers  the  liberation  of  steam  takes  place 
over  a  very  small  area  at  the  top  of  the  front  water  leg  and  the 
main  steam  connection  is  made  directly  above  this  point.  Under 
such  conditions,  large  quantities  of  water  would  be  thrown  into  the 
steam  pipe  if  some  provision  were  not  made  to  prevent  it.  The 


FIG.  130. 

usual  prevention  consists  of  a  baffle  plate  riveted  to  the  shell  and 
extending  over  the  top  of  the  water  leg  as  shown  in  Fig.  130. 
This  deflects  the  water  away  from  the  entrance  to  the  steam  pipe 
and  causes  the  steam  to  make  a  sharp  turn  at  its  upper  edge. 
A  dry  pipe  is  also  provided  for  further  separating  the  moisture. 
189.  Superheaters. — Superheaters  are  devices  for  heating 
steam  to  a  higher  temperature  than  that  at  which  it  is  formed. 
In  order  to  do  this,  the  steam  must  be  removed  from  the  presence 
of  water;  therefore  superheaters  are  so  located  that  the  steam 
will  have  to  pass  through  them  on  its  way  from  the  boiler  to  the 
engine.  If  steam  were  heated  above  its  saturation  temperature 
in  a  closed  vessel  its  pressure  would  increase,  but  this  is  prevented 
in  a  superheater  by  the  engine  taking  a  continuous  supply.  By 
superheating  steam,  its  amount  of  energy  is  increased  above 
that  which  it  would  have  if  it  were  only  saturated. 


246  STEAM  BOILERS 

Practically  all  superheaters  are  made  in  the  form  of  a  series  of 
pipes,  which  form  a  part  of  the  piping  system  between  the  boiler 
and  engine,  through  which  the  steam  must  flow  on  its  way  to 
the  engine.  The  pipes  may  be  either  plain  or  have  extended 
surfaces.  Those  having  extended  surfaces  are  usually  made  cf 
wrought  iron  or  steel  pipe  with  cast-iron  fins  fastened  to  them. 
Heat  is  applied  to  the  outside  of  the  pipes  while  the  steam  flowing 
through  the  inside  absorbs  it  and  has  its  temperature  raised. 
The  position  of  the  superheater  with  reference  to  the  boiler 
varies  with  different  superheaters.  In  this  country,  superheated 
steam  is  seldom  used  at  a  higher  temperature  than  500°  F.,  and 
450°  F.  is  perhaps  a  better  average,  while  in  Europe  600°  F.  is 
not  uncommon.  The  difference  in  practice  between  this  country 
and  Europe  is  due  to  the  fact  that  with  very  high  temperatures  of 
.  steam  the  ordinary  slide  and  Corliss  valves  of  engines,  as  used  in 
this  country,  are  liable  to  be  warped.  European  engines  are 
usually  supplied  with  a  type  of  valve  which  is  not  affected  very 
much  by  high  temperatures.  With  high  temperatures  some 
difficulty  is  experienced,  also,  with  the  lubrication  of  piston 
and  valve  rods.  A  steam  temperature  of  500°  F.  corresponds 
to  about  165°  of  superheat  at  100  Ib.  pressure  and  about  130° 
at  150  Ib.  pressure.  This  amount  of  superheat  insures  dry 
steam  at  cut-off  in  ordinary  forms  of  steam  engines,  and  as  the 
greatest  benefit  from  superheat  is  in  securing  dry  steam  during 
admission  to  the  engine  cylinder,  it  appears  that  the  amount  of 
superheat  mentioned  above  is  sufficient  with  present  practice  in 
this  country. 

Superheaters  may  be  located  directly  in  the  boiler  setting,  in 
a  flue  leading  from  the  boiler,  or  may  be  in  an  independent  setting 
and  fired  independently.  Standard  practice  in  this  country 
seems  to  favor  placing  the  superheater  directly  in  the  boiler  set- 
ting, from  80  to  90  per  cent  of  all  superheaters  installed  being  so 
located.  Wherever  located,  the  successful  operation  of  a  super- 
heater demands  that  it  possess  certain  qualities,  among  which 
are  safety,  efficient  use  of  heat,  freedom  for  expansion,  protection 
of  joints  from  direct  action  of  the  fire,  an  arrangement  whereby 
it  may  be  cut  out  and  cleaned,  both  internally  and  externally, 
and  ease  of  application  to  existing  plants  as  well  as  to  new  ones. 

Of  superheaters  placed  directly  in  the  boiler  setting  perhaps 
the  Foster,  the  Babcock  and  Wilcox,  and  the  Stirling  are  most 
widely  known  in  this  country. 


BOILER  ACCESSORIES 


247 


190.  Foster  Superheater. — The  application  of  a  Foster  super- 
heater to  an  Edge  Moor  water-tube  boiler  is  shown  in  Fig.  131  and 
the  construction  of  the  superheater  tubes  is  illustrated  in  Fig.  132. 
As  shown  in  the  above  figures,  the  Foster  superheater  consists 
of  a  series  of  U-shaped  tubes  connected  into  steel  headers  at  the 
ends.  The  tubes  are  double,  consisting  of  an  outer  steel  tube 
over  which  is  placed  a  cast-iron  covering  in  the  form  of  a  series 
of  fins,  and  a  steel  inner  tube  closed  at  both  ends  and  provided 


FIG.  131. — Foster  superheater. 

with  a  series  of  buttons  to  keep  it  centrally  located  with  respect 
to  the  outer  tube.  The  fins  on  the  outer  tube  serve  the  double 
purpose  of  protecting  the  steel  tube  against  being  burned,  and 
presenting  a  larger  surface  for  absorbing  heat.  Steam  flows 
through  the  space  between  the  inner  and  outer  tubes,  the  inner 
one  serving  to  direct  the  steam  along  the  surface  of  the  outer 
tube,  thus  bringing  it  into  direct  contact  with  the  heating  surface. 
Fig.  131  shows  the  superheater  placed  between  the  first  and 
second  passes  of  the  boiler.  This  is  a  common  location  when 
applied  to  water-tube  boilers,  though  it  must  not  be  inferred  that 


248 


STEAM  BOILERS 


this  is  the  only  location  to  which  it  is  suited  nor  the  only  type  of 
boiler  to  which  it  may  be  applied.  The  simplicity  and  small 
space  occupied  by  this  superheater  adapt  it  to  any  style  of  boiler. 
When  applied  to  water-tube  boilers  in  which  the  flue  gases  pass 
across  the  tubes,  it  is  usually  placed  as  shown  in  Fig.  131;  while  in 
those  water-tube  boilers  which  have  the  flue  gases  passing  along 
the  tubes,  it  is  usually  located  on  top  of  the  setting  and  near  the 
steam  drum.  In  the  Stirling  boiler,  it  is  located  between  the 
second  and  third  banks  of  tubes;  and  in  return  fire-tube  boilers, 
it  is  located  at  the  back  of  the  combustion  chamber  where  the 


FIG.  132. 

hot  gases  must  pass  through  it  before  turning  into  the  tubes. 
Although  the  Foster  superheater  is  often  conveniently  located 
below  the  water  line  of  a  boiler,  it  is  not  necessary  to  flood  it  with 
water  when  the  flow  of  steam  from  the  boiler  is  reduced,  because 
the  cast-iron  covering  prevents  injury  to  the  tubes  from  this 
cause.  Since  the  superheater  is  never  flooded  with  water  it  is 
not  necessary  to  make  provision  for  cleaning  the  interior  of  the 
tubes. 

191.  Babcock  and  Wilcox  Superheater. — The  application  of  a 
Babcock  and  Wilcox  superheater  to  a  Babcock  and  Wilcox  water- 
tube  boiler  is  shown  in  Figs.  133  and  134.  This  superheater  is 
similar  in  shape  to  the  Foster  superheater  just  described,  but 
differs  from  it  in  construction.  The  Babcock  and  Wilcox  super- 


BOILER  ACCESSORIES 


249 


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o°o°ou 


250 


STEAM  BOILERS 


heater  consists  of  a  number  of  single  U-shaped  steel  tubes  with 
the  ends  connected  into  headers.  The  saturated  steam  is  sup- 
plied to  the  top  header  through  a  short  dry-pipe  located  near  the 
top  of  the  steam  space.  The  connection  between  the  steam 
space  and  the  superheater  is  made  by  two  tubes  which  pass  down 
through  the  water  space  and  through  the  bottom  of  the  steam 
and  water  drum.  From  the  top  header,  the  steam  flows  through 
the  tubes,  receiving  heat  and  becoming  superheated.  The 
superheated  steam  is  taken  from  the  bottom  header. 


FIG.  135. — Stirling  superheater. 

Since  this  superheater  is  made  of  steel  tubes,  and  is  subjected 
to  a  high  temperature,  provision  must  be  made  for  flooding  it 
when  steam  is  being  raised  or  at  such  other  times  as  the  flow  of 
steam  through  it  is  small.  This  is  provided  for  by  connecting 
the  lower  header  with  the  steam  space  by  means  of  a  pipe,  which 
passes  through  the  rear  wall  of  the  setting  and  into  the  steam 
drum  below  the  water  line,  as  shown  in  Fig.  133.  When  it  is 


BOILER  ACCESSORIES 


251 


desired  to  flood  the  superheater,  a  valve  in  this  pipe  is  opened 
and  the  water  will  be  forced  into  superheater  tubes.  Any  steam 
that  may  be  formed  in  the  superheater  while  it  is  flooded  will  pass 
out  of  the  top  header  and  into  the  steam  space  of  the  boiler. 
When  ready  to  resume  operations  the  water  may  be  drained 
from  the  superheater  by  closing  the  flooding  valve  and  opening 
a  drain  cock  in  the  flooding  pipe. 

192.  Stirling  Superheater. — The  Stirling  superheater,  shown 
in  Fig.  135,  is  designed  for  use  only  with  the  Stirling  boiler.  It 
consists  of  two  drums  connected  by  a  number  of  2-in.  seamless 
steel  tubes,  and  is  placed  behind  the  first  bank  of  boiler  tubes, 


FIG.  136. 

in  the  position  occupied  by  the  second  bank  in  the  regular 
Stirling  boiler.  The  joints  between  the  tubes  and  the  drums  are 
protected  by  a  layer  of  asbestos  to  prevent  burning  at  these 
points.  The  upper  drum  of  the  superheater  is  connected  to  the 
steam  spaces  of  the  boiler,  from  which  it  receives  its  supply  of 
saturated  steam.  The  upper  and  lower  drums  are  divided  into 
compartments  so  the  steam  is  forced  to  pass  through  the  tubes 
four  times  on  its  way  through  the  superheater.  A  cross-section 
of  the  superheater  showing  the  arrangement  of  the  compartments 
is  shown  in  Fig.  136.  The  saturated  steam  enters  one  of  the 
end  compartments  of  the  top  drum  and  superheated  steam  is 
delivered  to  the  other  end  compartment  of  the  top  drum.  Each 
compartment  contains  either  a  manhole  or  a  removable  partition 


252 


STEAM  BOILERS 


so  that  all  parts  of  the  drums  are  accessible  for  cleaning  the  tubes. 

Arrangement  for  flooding  the  superheater  is  made  by  a  pipe 
and  valves  on  the  outside  of  the  boiler  setting,  shown  dotted  in 
Fig.  135.  The  same  connection  to  the  lower  drum  allows  the 
superheater  to  be  drained. 

The  arrangement  of  the  superheater  shown  in  Fig.  135  is 
designed  to  give  about  250°  of  superheat.  When  only  about 
100°  of  superheat  is  desired,  the  superheater  is  placed  behind  the 
last  bank  of  boiler  tubes.  The  Stirling  superheater  is  also 
designed  in  a  form  to  be  separately  fired. 


FIG.  137. — Heine  superheater. 

193.  Heine  Superheater. — The  Heine  superheater,  shown  in 
Fig.  137,  is  heated  directly  by  the  hot  gases  from  the  furnace, 
though  it  differs  from  the  ones  just  described  in  that  it  is  not 
placed  directly  in  one  of  the  passes  but  is  located  at  the  top  of 
the  setting  by  the  side  of  the  steam  drum. 

This  superheater  is  made  of  a  number  of  U-shaped  seamless 
steel  tubes  ending  in  a  steel  header.  The  header  is  divided  into 
three  compartments  by  partitions  which  force  the  steam  to  flow 
through  the  tubes  four  times  in  passing  through  the  superheater. 


BOILER  ACCESSORIES  253 

Saturated  steam  enters  the  bottom  compartment  and  the 
superheated  steam  is  drawn  from  the  top  one.  A  hand  hole 
with  inside  cover  plates  is  located  in  the  front  of  the  header 
opposite  each  tube,  to  allow  access  to  the  tubes  for  repairing 
them.  Since  the  superheater  is  placed  above  the  setting,  it  is 
not  necessary  to  flood  it  and,  therefore,  the  inside  of  the  tubes 
will  not  require  cleaning.  Hollow  stay  bolts  are  used  for  joining 
the  two  end  plates  of  the  header.  By  inserting  a  steam  blower 
through  the  hollow  stay  bolts,  soot  may  be  blown  from  the  outside 
of  the  superheater  tubes.  The  shape  of  the  tubes  allows  freedom 
for  expansion. 

The  Heine  superheater  receives  its  heat  from  gases  taken 
directly  from  the  furnace.  In  order  to  do  this,  the  superheater  is 
enclosed  in  a  brick  setting  which  has  two  openings  in  the  bottom, 
one,  not  shown  in  the  illustration,  connecting  directly  with  the 
furnace  and  the  other,  which  is  shown  in  the  illustration,  connect- 
ing with  the  smoke  pass  which  leads  to  the  chimney.  A  damper  is 
provided  in  the  latter  opening  for  throwing  the  superheater  out  of 
operation.  A  portion  of  the  hot  gases  from  the  furnace  are 
taken  into  the  superheater  setting  near  the  rear  end,  pass  along 
the  tubes  and  leave  near  the  front  end. 

194.  Schmidt  Superheater. — One  of  the  most  commonly  used 
independently  fired  superheaters  is  the  Schmidt,  shown  in  Fig. 
138.  The  superheater  consists,  of  two  sets  of  coils  arranged 
so  the  steam  flows  first  through  one  and  then  through  the  other. 
The  saturated  steam  enters  at  the  top  of  the  upper  set  of  tubes, 
passes  through  this  set,  and  leaves  at  the  bottom.  It  is  then 
carried  by  the  pipe  D  to  the  bottom  of  the  lower  set  of  tubes, 
and  passes  through  these,  the  superheated  steam  leaving  at  the 
top  of  the  lower  set  of  tubes  through  the  outlet  E.  This  system  of 
passing  the  steam  through  the  tubes  combines  what  is  called  the 
concurrent  and  the  counter-current  systems;  the  counter- 
current  system,  in  which  the  steam  flows  in  the  opposite  direction 
to  the  hot  gases,  is  used  in  the  upper  set  of  tubes;  and  the 
concurrent,  in  which  the  steam  flows  in  the  same  direction  as  the 
hot  gases,  is  used  in  the  lower  set.  While  the  counter-current 
system  gives  high  efficiency,  it  is  open  to  the  objection  that  the 
hot  gases  from  the  fire  meet  the  tubes  where  the  superheated 
steam  is  hottest,  and  hence  the  tubes  are  liable  to  be  burned 
through.  The  concurrent  system  overcomes  this  drawback, 
but  does  not  secure  maximum  efficiency.  The  arrangement 


254 


STEAM  BOILERS 


used  in  the  Schmidt  superheater  combines  the  two  systems, 
giving  a  very  good  efficiency  without  the  danger  of  burning  the 
tubes. 

The  junction  boxes  on  the  Schmidt  superheater  are  placed 
outside  the  setting  where  they  will  not  be  in  contact  with  the  fire 


FIG.  138. — Schmidt  separately  fired  superheater. 

and  where  they  will  be  more  accessible.  Should  a  tube  become 
burned,  its  ends  may  be  stopped  with  blank  flanges,  and  the 
superheater  continued  in  operation  until  such  time  as  the  tube 
may  be  replaced. 

The  advantages  of  independently  fired  superheaters  are  that 
they    may  be    placed   at    any  point   desired,  repairs   may  be 


BOILER  ACCESSORIES  255 

made  without  shutting  down  the  boilers,  and  the  degree  of 
superheat  may  be  varied  independently  of  the  performance  of 
the  boiler.  Its  disadvantages  are  the  extra  space  required, 
extra  piping  required,  separate  firing  with  the  losses  attending 
two  furnaces  instead  of  one,  and  extra  labor  required. 

It  must  not  be  thought  that  because  a  superheater  is  located 
in  the  path  of  the  flue  gases,  it  does  not  require  extra  fuel  to  heat 
it.  The  higher  the  temperature  to  which  the  steam  is  super- 
heated, the  more  fuel  will  be  required,  as  shown  in  the  following 
table : 

Degree  of  superheat  Additional  fuel  needed 
75°  5  per  cent 

100°  7  per  cent 

150°  11  per  cent 

200°  15  per  cent 

250°  20  per  cent 

Thus  if  a  boiler  is  using  4  Ib.  of  fuel  to  produce  a  pound  of 
saturated  steam,  it  will  require  4X1.15=4.60  Ib.  to  produce  a 
pound  of  superheated  steam  when  the  steam  is  superheated  200°. 

195.  Damper  Regulators. — To  keep  the  pressure  of  the  steam 
constant,  the  fireman  must  move  the  damper,  opening  it  when  the 
pressure  falls  or  closing  it  when  it  rises.  If  more  steam  is  re- 
quired than  a  boiler  is  producing,  the  pressure  will  gradually 
fall  and,  to  prevent  this,  coal  must  be  burned  at  a  higher  rate. 
This  is  accomplished  by  opening  the  damper  and  thus  allowing 
more  air  to  be  drawn  through  the  fire,  consuming  more  coal. 
Should  the  demand  for  steam  decrease,  the  steam  pressure  would 
rise,  and  the  damper  should  be  closed  to  accommodate  the  new 
conditions.  To  do  this  automatically  and  to  keep  the  pressure 
more  nearly  uniform,  the  damper  regulator  has  been  invented. 
The  draft  caji  be  controlled  by  a  regulator  so  that  a  practically 
constant  steam  pressure  may  be  maintained.  Damper  regulators 
are  economical  and  very  useful,  especially  in  plants  where  the 
demand  for  steam  fluctuates  rapidly.  In  the  most  common 
form,  the  boiler  steam  presses  on  a  diaphragm  which  is  connected 
to  a  lever  that  controls  a  small  water  valve.  If  the  steam  pres- 
sure falls,  the  water  valve  is  opened,  permitting  water  to  escape 
from  a  hydraulic  cylinder,  thus  lowering  the  plunger  and  opening 
the  damper.  If  the  steam  pressure  rises,  water  is  admitted  to 
the  cylinder,  which  raises  the  plunger  and  closes  the  damper. 
When  properly  adjusted  they  work  in  a  very  satisfactory  manner. 


256 


STEAM  BOILERS 


A  damper  regulator  of  this  type  is  shown  in  Fig.  139.  Full 
boiler  pressure  acts  at  all  times  upon  a  diaphragm  in  the  chamber 
A  and  raises  or  lowers  the  weight  W  attached  to  the  arm  D. 
The  arm  D  moves  a  valve  V  which  controls  the  supply  of  water 
to  the  chamber  B.  A  diaphragm  in  B  raises  and  lowers  the 
lever  E  as  the  water  pressure  varies.  The  end  of  E  is  connected 
with  the  damper.  The  steam  diaphragm  moves  only  .01  in.  and 
the  water  diaphragm  moves  .5  in.  A  drop  of  1/2  Ib.  in  the  steam 
pressure  is  sufficient  to  cause  the  damper  to  be  opened  to  its 
maximum  opening. 


FIG.  139. — Damper  regulator. 

196.  Feed  Pumps. — Water  is  fed  to  boilers  by  means  of  both 
pumps  and  injectors.  In  determining  which  of  these  two  methods 
shall  be  used,  such  things  as  quantity  of  water  to  be  dealt  with, 
the  temperature  of  the  supply,  the  height  to  be  lifted  and  con- 
venience of  handling  have  to  be  considered. 

When  large  quantities  of  water  have  to  be  dealt  with,  as,  for 
instance,  in  feeding  a  battery  of  boilers,  pumps  are  commonly 
used,  while  for  supplying  single  boilers,  injectors  are  often  more 
convenient.  Injectors  are  more  tricky  to  operate  than  pumps, 
but  they  are  much  more  efficient,  as  practically  all  the  heat 
supplied  to  them  is  used  either  to  move  the  feed  water  or  to  raise 
its  temperature.  While  a  pump  is  much  more  reliable  than  an 
injector  it  is  very  wasteful  of  steam.  Its  efficiency  may  be  im- 
proved in  many  cases  by  using  the  exhaust  to  heat  the  feed  water. 
If  properly  arranged,  a  pump  will  handle  water  of  almost  any 
temperature  below  the  boiling-point.  On  the  other  hand,  110° 
F.  is  about  as  high  a  feed-water  temperature  as  an  injector  can 
handle,  and  it  must  be  less  than  this  if  the  water  is  lifted  a  few 
feet. 


BOILER  ACCESSORIES 


257 


Boiler  feed  pumps  are  usually  either  single  or  duplex,  direct 
acting.  In  the  single  pumps  there  is  one  steam  and  one  water 
cylinder  placed  in  line  with  each  other,  both  pistons  being  on  a 
single  piston  rod.  Duplex  pumps  have  two  steam  cylinders 
placed  beside  each  other  and  two  water  cylinders  similarly  placed. 
This  makes  the  duplex  pump  resemble  two  independent  single 
pumps  placed  one  beside  the  other.  In  the  duplex  pump,  the 
steam  valve  of  one  is  operated  from  the  piston  rod  of  the  other, 
thus  making  it  almost  impossible  for  the  pump  to  stop  on  "center" 
as  single  pumps  sometimes  do.  Duplex  pumps  have  practically 


FIG.  140. — Single  direct  acting  feed  pump. 

twice  the  capacity  of  single  pumps  of  the  same  size  cylinder,  and 
they  use  practically  twice  as  much  steam. 

There  are  two  forms  of  single  direct  acting  boiler  feed  pumps, 
which  differ  from  each  other  in  the  operation  of  the  steam  valve. 
In  one  of  these,  the  valve  is  operated  by  a  system  of  levers  out- 
side the  cylinder  and  in  the  other  form,  the  valve  is  operated 
entirely  by  the  steam  inside  the  steam  chest  and  there  are  no 
working  parts  on  the  outside. 

A  cross-sectional  view  of  a  single  direct  acting  boiler  feed 
pump,  with  valves  controlled  from  outside  the  cylinder,  is  shown 
in  Fig.  140.  The  construction  may  be  described  as  follows: 
An  auxiliary  piston  works  in  the  steam  chest  and  drives  the  main 
valve.  This  auxiliary  or  "  chest-piston,"  as  it  is  called  is  driven 


258 


STEAM  BOILERS 


backward  and  forward  by  the  pressure  of  the  steam,  and  as  it 
moves,  carries  with  it  the  main  valve,  which  controls  the  supply 
of  steam  to  the  main  steam  cylinder  and  thus  operates  the  pump. 
The  main  valve  is  B-shaped  and  works  on  a  flat  seat.  The  main 
piston  rod  is  supplied  with  a  small  roller  which  engages  at  the 
end  of  each  stroke  with  one  or  the  other  end  of  the  rocker  which 
is  pivoted  to  the  middle  of  the  pump  frame.  This  rocker  is  con- 
nected to  the  valve  rod  in  such  manner  that  when  the  end  of  the 
rocker  is  raised  a  slight  turning  movement  is  given  to  the  chest- 
piston.  The  turning  movement  places  small  steam  ports,  which 
are  located  in  the  under  side  of  the  chest-piston,  in  proper  con- 


FIG.   141. — Single  direct  acting  feed  pump. 

tact  with  corresponding  ports  cut  in  the  steam  chest.  The  steam 
entering  through  the  port  at  one  end  and  filling  the  space  between 
the  chest-piston  and  the  head,  drives  the  chest-piston  to  the  end 
of  its  stroke  and  carries  the  main  valve  with  it.  When  the 
chest-piston  has  traveled  a  certain  distance,  a  port  on  the  opposite 
end  is  uncovered  and  steam  enters  and  stops  it  by  giving  it  the 
necessary  cushion.  In  other  words,  when  the  turning  movement 
is  given  to  the  auxiliary  or  chest-piston  by  the  mechanism,  it 
opens  the  port  to  steam  admission  on  one  end,  and  at  the  same 
time  opens  the  port  on  the  other  end  to  exhaust. 


BOILER  ACCESSORIES  259 

A  single  direct  acting  feed  pump  with  valve  controlled  entirely 
by  steam  pressure,  and  no  outside  mechanism,  is  shown  inFig.  141. 
Referring  to  this  figure,  A  is  the  steam  cylinder;  C  the  piston; 
L  the  steam  chest;  F  the  chest  plunger,  the  right-hand  end  of 
which  is  shown  in  section;  G  the  slide  valve ;  H  a  lever  by  means 
of  which  the  steam-chest  plunger  F  may  be  reversed  by  hand 
when  necessary;  I  I  are  reversing  valves;  K  K  are  reversing 
valve-chamber  bonnets;  E  E  are  exhaust  ports  leading  from  the 
ends  of  the  steam  chest  direct  to  the  main  exhaust  and  closed  by 
the  reversing  valves  7  7. 

In  operation,  the  piston  C  is  driven  by  steam  admitted  under 
the  slide  valve  G,  which,  as  it  is  shifted  backward  and  forward 
alternately  connects  opposite  ends  of  the  cylinder  A  with  the 
live  steam  pipe  and  exhaust.  This  slide  valve  G  is  shifted  by  the 
auxiliary  plunger  F.  F  is  hollow  at  the  ends,  which  are  filled 
with  steam,  and  this,  issuing  through  a  hole  in  each  end,  fills  the 
space  between  it  and  the  heads  of  the  steam  chest  in  which  it 
works.  The  pressures  at  the  ends  of  the  plunger  F  being  equal, 
it  is  ordinarily  balanced  and  motionless;  but  when  the  main 
piston  C  has  traveled  far  enough  to  strike  and  open  the  reverse 
valve  7,  the  steam  exhausts  through  the  port  E  from  behind 
that  end  of  the  plunger  F,  passing  into  the  main  exhaust  by  the 
passage  shown  dotted,  and  thus  reverses  the  pump.  In  its  move- 
ment, the  plunger  F  acts  as  a  slide  valve  to  close  the  port  E, 
and  is  cushioned  on  the  steam  confined  between  the  ports  and 
steam-chest  cover.  The  reverse  valves  7  7  are  closed,  as  soon  as 
the  piston  C  leaves  them  by  a  constant  pressure  of  steam,  con- 
veyed directly  from  the  steam  chest  through  the  ports  shown  by 
the  dotted  lines. 

197.  Duplex  Pumps. — A  duplex  pump  consists  of  two  single 
pumps  placed  side  by  side  and  working  in  parallel  between  the 
suction  and  discharge  sides.  The  steam  valve  of  one  side  is 
operated  from  the  piston  rod  of  the  other  side,  causing  the  pistons 
to  move  in  opposite  directions.  One  piston  is  always  in  motion 
while  the  other  is  stopped  at  the  end  of  the  stroke,  thus  providing 
a  practically  continuous  flow  of  water  from  the  discharge.  Fig. 
142  shows  the  general  form  of  a  duplex  pump,  while  Fig.  143  is  a 
cross-section  of  the  same  pump,  showing  the  details  of  its 
construction. 

The  steam  valves  of  a  duplex  pump  are  very  similar  to  those 
of  a  plain  slide-valve  steam  engine,  but  they  do  not  lap  over  the 
22 


260 


STEAM  BOILERS 


steam  or  exhaust  ports  when  the  valve  is  in  the  middle  of  its 
travel.  In  order  to  make  the  valve-travel  as  small  as  possible, 
thus  reducing  its  friction,  and  at  the  same  time  give  it  sufficient 
bearing  surface  to  prevent  leakage  of  live  steam  from  the  admis- 


FIG.  142. — Duplex  pump. 


AIR   CHAMBER 


DISCHARGE 


FIG.  143. — Cross-section  of  duplex  pump. 

sion  to  the  exhaust  sides,  the  exhaust  ports  are  made  separate 
from  the  admission  ports,  but  placed  very  close  to  them.  The 
separate  exhaust  ports  also  give  a  simple  means  of  cushioning  the 
piston  near  the  end  of  its  stroke,  bringing  it  to  rest  without 


BOILER  ACCESSORIES 


261 


shock  or  pounding,  and  preventing  it  from  striking  the  heads  of 
the  cylinder.  When  a  valve  has  no  lap  on  either  the  steam  or 
exhaust  sides,  it  closes  the  exhaust  at  the  same  time  that  it  opens 
the  admission;  such  a  valve  would  have  to  act  quickly  and  at 
the  end  of  the  stroke.  This  would  not  be  advisable  in  a  duplex 
pump  where  the  valve  on  one  side  is  operated  from  the  piston  on 
the  other,  as  the  pistons  would  reach  the  ends  of  their  strokes 
together  and  there  would  be  danger  of  the  pump  stopping  on 
"  center."  To  avoid  this  difficulty  the  valves  are  given  consider- 
able lost  motion  by  allowing  sufficient  clearance  between  the  lock- 


FIG.  144. — Steam  cylinder  and  valve  of  duplex  pump. 

nuts  on  the  valve  stem.  This  permits  the  valve  to  remain  station- 
ary until  the  piston  has  nearly  completed  its  stroke,  and  renders 
it  impossible  for  the  pistons  to  stop  on  center  as  they  do  not  reach 
their  extreme  positions  at  the  same  time;  therefore  one  of  them 
is  always  in  a  position  to  be  moved  by  the  steam. 

Fig.  144  shows  a  cross-section  of  one  cylinder  and  valve  of  a 
duplex  pump,  with  the  piston  beginning  the  forward  stroke.  The 
valve  has  been  moved  forward  by  the  other  piston  rod  so  as  to 
admit  steam  behind  the  piston  and  open  the  exhaust  from  the 
front  end  of  the  cylinder.  As  the  piston  moves  forward,  the 
valve  remains  stationary,  due  to  the  lost  motion  between  it  and 
its  valve  rod.  When  the  piston  is  nearly  at  the  end  of  its  stroke 
the  other  piston  rod  begins  to  move  the  valve  backward,  closing 


262  STEAM  BOILERS 

the  admission  port  P  and  the  exhaust  port  E.  By  this  time  the 
piston  has  covered  the  exhaust  port  on  the  front  end  of  the  cylin- 
der and  compresses  the  remaining  steam  into  the  end  of  the  cylin- 
der, thus  stopping  the  piston  gradually.  By  the  time  the  piston 
has  reached  the  end  of  its  stroke  the  valve  has  been  moved  back 
enough  to  uncover  the  admission  port  on  the  front  end  and  open 
the  exhaust  port  on  the  back  end,  which  causes  the  piston  to 
start  on  its  back  stroke. 

The  water  ends  of  both  single  and  duplex  pumps  are  practically 
alike  and  are  illustrated  in  Figs.  140  and  143.  They  consist  of  a 
cylinder  fitted  with  either  a  piston  or  a  plunger,  and  two  sets  of 
valves,  the  lower  ones  being  the  suction  and  the  upper  ones  the 
discharge  valves.  On  the  forward  stroke  of  the  plunger,  the 
pressure  in  the  right-hand  end  of  the  cylinder  is  reduced  until 
water  flows  in  through  the  suction  valves,  filling  the  cylinder. 
On  the  back  stroke  the  water  exerts  a  pressure  on  top  of  the  suc- 
tion valves,  holding  them  closed.  The  pressure  will  increase  until 
it  is  great  enough  to  overcome  the  pressure  on  top  of  the  delivery 
valves,  when  these  will  open  and  allow  the  water  in  the  cylinder 
to  be  discharged. 

The  pistons  or  plungers  of  double  acting  pumps  require  pack- 
ing to  prevent  water  leaking  from  one  side  to  the  other  and  thus 
reducing  the  amount  of  water  pumped.  As  leaks  in  the  packing 
are  not  easily  detected,  great  care  should  be  used  to  prevent  them. 
When  cold  water  is  to  be  pumped,  the  packing  is  usually  of  a  soft 
material,  but  for  hot  water  a  metallic  packing  is  better. 

A  common  method  of  packing  water  pistons  with  soft  packing 
is  illustrated  in  Fig.  145.  The  packing  consists  of  four  rings  of 
fibrous  material  held  between  the  two  halves  of  the  piston.  By 
screwing  together  the  two  halves  of  the  piston  the  packing  is 
squeezed  out  until  it  makes  a  water-tight  fit  against  the  sides  of 
the  cylinder.  In  cutting  ring  packing  of  this  kind,  the  length 
of  each  piece  should  be  shorter  than  the  circumference  of  the 
groove  into  which  it  is  to  be  placed.  The  reason  for  this  is  that 
the  packing  is  cut  dry,  and  after  becoming  wet  it  lengthens  and, 
if  cut  long  enough  to  reach  around  the  groove,  it  will  grip  the 
cylinder  too  hard  after  it  has  become  wet.  To  allow  for  this, 
the  packing  should  be  cut  short  by  an  amount  equal  to  the  thick- 
ness of  the  packing.  Another  method  of  placing  the  packing  for 
a  water  piston  is  shown  in  Fig.  146.  In  this  method,  a  number  of 
grooves  are  cut  in  the  circumference  of  the  piston  and  a  single 


BOILER  ACCESSORIES 


263 


strand  of  packing  placed  in  each  one.  No  provision  is  made  for 
tightening  the  packing  in  this  method.  A  cup  leather  packing  is 
illustrated  in  Fig.  147.  In  this  method  of  packing  two  leather 
washers  are  clamped  into  the  piston  and  have  the  edges  folded 
out  in  opposite  directions  along  the  sides  of  the  piston.  A  special 
mold  or  clamp  is  used  for  shaping  the  leather  washers  correctly. 
Fig.  148  shows  the  method  of  packing  a  water  plunger.  This 


FIG.  145. 


FIG.  146. 


device  amounts  to  an  internal  stuffing  box  and  a  pump  packed  in 
this  manner  is  said  to  be  "  inside  packed."  An  "  outside  packed  " 
plunger  is  one  in  which  the  plunger  extends  through  the  head  of 
the  cylinder  and  is  packed  on  the  outside  with  a  stuffing  box  in  a 
manner  similar  to  the  packing  of  a  steam  engine  piston  rod. 
When  the  pump  is  double  acting,  the  water  cylinder  is  divided 
into  two  parts  by  a  metal  partition  extending  across  its  center. 


FIG.  147. 

With  this  method  of  packing  it  is  necessary  to  use  two  plungers, 
which  are  fastened  together  with  tie  rods  on  the  outside  of  the 
cylinder  in  order  to  force  the  plungers  to  move  together.  Fig. 
149  shows  an  outside  packed  plunger  pump,  the  tie  rods  being 
shown  dotted. 

Since  the  movement  of  the  pump  piston  is  more  or  less  inter- 
mittent, the  flow  of  water  through  the  discharge  would  vary 
unless  an  air  chamber  were  connected  to  the  discharge  side  of  the 


264 


STEAM  BOILERS 


pump.  During  certain  portions  of  the  stroke,  the  pressure  devel- 
oped is  greater  than  normal,  and  the  excess  pressure  at  such 
times  compresses  the  air  which  is  contained  in  the  air  chamber. 
When  the  pressure  falls  below  normal,  the  air  expands  and 
forces  water  through  the  discharge.  Thus  the  air  chamber  tends 


FIG.  148. — Inside  packed  water  plunger. 

to  produce  a  steady  flow  of  water  through  the  discharge  and 
prevents  shock  in  the  piping.  The  size  of  the  air  chamber  will 
depend  upon  the  ordinary  running  speed  of  the  pump,  being 
larger  for  high-speed  pumps  than  for  low-speed  ones.  '  On  single 
cylinder  pumps  the  air  chamber  should  be  from  two  to  three 
and  one-half  times  the  volume  displaced  at  each  stroke  of  the 


FIG.  149. — Outside  packed  water  plunger. 

plunger,  and  for  duplex  pumps  it  should  be  from  one  to  two 
and  one-half  times  the  plunger  displacement.  The  larger  the 
chamber  the  more  uniform  will  be  the  discharge  pressure. 

A  vacuum  chamber  placed  on  the  suction  side  of  a  pump 
assists  in  securing  a  uniform  flow  of  water  through  the  suction 
pipe  and  in  filling  the  cylinder  completely  at  each  stroke.  The 
vacuum  chamber  should  have  a  volume  slightly  greater  than  that 
of  the  suction  pipe,  and  should  have  great  length  rather  than  great 


BOILER  ACCESSORIES 


265 


FIG.  150. 


diameter.  A  good  location  for  the  vacuum  chamber  is  shown  in 
Fig.  150. 

With  a  tight  suction  pipe  and  cold  water,  a  pump  may  lift 
its  supply  of  water  several  feet,  but  if  the  pump  is  to  handle  hot 
water  the  supply  should  be  above  the 
level  of  the  pump,  so  that  the  water 
may  run  into  the  water  cylinder  by  the 
force  of  gravity.  If  the  supply  is  placed 
below  the  pump,  the  suction  stroke  will 
reduce  the  pressure  on  the  supply,  thus 
lowering  its  boiling-point  and  causing 
the  water  to  give  off  large  quantities  of 
vapor,  which  will  flow  into  the  cylinder 
and  prevent  its  filling  with  water. 

The    water   piston   of   a   boiler  feed 
pump  is  made  smaller  in  diameter  than 

the  steam  piston,  in  order  that  a  higher  pressure  may  be  de- 
veloped in  the  water  cylinder  than  is  supplied  in  the  steam 
cylinder.  This  is  done  in  order  that  the  boiler  pressure  may 
be  used  in  the  steam  cylinder,  and  the  water  deliverd  at  a 
high  enough  pressure  to  enter  the  boiler  and  overcome  the 
resistance  of  the  piping  system. 

If  the  water  cylinder  were  completely  filled  with  water  at  each 
suction  stroke  and  there  were  no  leakage,  the  amount  of  water 
pumped  at  each  stroke  would  be  equal  to  the  piston  displacement. 
Because  of  the  cylinder  not  filling  completely  at  each  suction 
stroke  and  because  of  unavoidable  leak,  the  amount  of  water 
delivered  is  always  less  than  the  piston  displacement.  The 
difference  between  the  piston  displacement  and  the  volume  of 
water  actually  pumped,  expressed  as  a  per  cent  of  the  piston 
displacement,  is  called  the  "slip."  Thus,  if  the  piston  dis- 
placement of  a  certain  pump  is  200  cu.  ft.  per  minute  and  the 
pump  actually  delivers  only  170  cu.  ft.  per  minute,  the  slip  is 
200-170  30 


1K 
200      =200  Per   cen^- 


..      .  ... 

slip   in   a   new  pump  will 


usually  amount  to  about  10  per  cent  and  increases  with  the  length 
of  time  the  pump  is  used,  due  to  increased  leakage. 

In  determining  the  size  of  pump  to  be  used  with  a  certain 
size  boiler,  the  amount  of  water  used  by  the  boiler  when  working 
at  its  rated  capacity  should  first  be  determined,  and  a  size  of 
pump  chosen  which,  when  working  at  40  strokes  per  minute,  will 


266 


STEAM  BOILERS 


have  a  piston  displacement  equal  to  the  volume  of  water  required. 
By  basing  the  capacity  of  the  pump  on  40  strokes  per  minute, 
sufficient  allowance  will  be  made  for  the  slip  of  the  pump  and 
for  any  overload  that  may  come  on  the  boiler. 

To  illustrate  this  method  of  determining  the  size  of  feed  pump, 
suppose  a  pump  is  to  be  purchased  to  supply  water  to  a  200-h.p. 
boiler  which  generates  steam  at  150  Ib.  gage  pressure  from  feed 
water  at  130°. 

200  h.p.will  require  200X34.5  =  6900  Ib.  of  water  from  and  at 
212°  per  hour.  By  referring  to  the  table  of  Factors  of  Evaporation 
in  Chapter  VIII  the  factor  of  evaporation  for  150  Ib.  and  130° 
is  found  to  be  1.134  and  the  water  actually  required  by  the  boiler 
will  be 

6085  Ib.  per  hour  or  —   r-  =  10  1  .4  Ib.  per  minute.     Since  a 
oU 


cubic  foot  of  hot  water  weighs  about  60  Ib.,  101.5  Ib.  will  occupy 
a  volume  of  101.5^60.  =  1.69  cu.  ft.  or  1.69X1728  =2910  cu.  in. 

If  the  pump  is  to  run  40  strokes  per  minute,  its  piston  dis- 
placement per  stroke  will  be  2910  -=-40  =  72.  75  cu.  in. 

A  gallon  of  water  contains  231  cu.  in.;  therefore  the  pump 
must  have  a  capacity  of  72.75-^231  =.315  gallons  per  stroke. 
Referring  to  the  table  of  pump  sizes  below  we  see  that  a  5J  in. 
X3}  in.  X7  in.  pump  will  have  a  displacement  of  .34  gallons 
per  stroke  and  will  therefore  be  large  enough. 

TABLE  OF  SIZES  AND  CAPACITIES  OF  SINGLE  BOILER  FEED  PUMPS 


steam 
cyl., 
inches 

Diam. 
water  cyl., 
inches 

Length  of 
stroke, 
inches 

Gal.  per 
stroke 

Diam. 
steam  cyl., 
inches 

Diam. 
water  cyl., 
inches 

Length  of 
stroke, 
inches 

Gals, 
per 
stroke 

24 

1ft 

3 

.023 

74 

5 

10 

.85 

3 

U 

3 

.031 

8 

5 

12 

1.02 

3i 

2 

4 

.05 

10 

6 

12 

1.47 

34. 

21 

4 

.07 

12 

7 

12 

2.00 

4 

2* 

5 

.11 

12 

8 

12 

2.61 

5 

31 

7 

.25 

16 

10 

16 

5.44 

5* 

31 

7 

.34 

18 

12 

24 

11.75 

7 

4 

7 

.39 

20                   14 

24 

16.00 

7 

44 

10 

.69 

24                   16 

24 

20.80 

In  specifying  the  size  of  a  pump,  the  first  dimension  refers  to  the 
diameter  of  the  steam  cylinder,  the  second  dimension  refers  to  the 
diameter  of  the  water  cylinder,  and  the  third  dimension  to  the 
common  length  of  stroke. 


BOILER  ACCESSORIES  267 

The  pipe  connections  on  both  the  suction  and  delivery  sides 
of  a  pump  should  be  as  short  and  direct  as  possible,  and  the  steam 
connection  made  directly  to  the  steam  space  of  the  boiler  so  that 
steam  may  be  delivered  to  the  pump  even  when  the  main  valve 
on  the  boiler  is  closed. 

Suction  pipes  should  be  at  least  as  large  as  the  pump  opening, 
and  if  the  suction  pipe  is  long  or  has  many  bends,  it  should  be 
even  larger.  A  means  of  priming  or  charging  the  suction  pipe 
for  starting  is  also  desirable.  This  may  easily  be  done  by  con- 
necting the  discharge  side  to  the  suction  side  by  a  small  by-pass 
fitted  with  a  valve.  The  bottom  of  the  suction  pipe  should  be 
fitted  with  a  strainer  and  a  foot  valve  to  prevent  foreign  sub- 
stances entering  the  pump.  It  is  especially  important  that  there 
be  no  leaks  in  the  suction  pipe  and,  to  this  end,  the  joints  should  be 
very  carefully  made  when  erecting  the  piping. 

198.  Injectors. — Injectors  are  often  used  with  small  boilers 
and  in  some  cases  with  large  ones,  where  there  is  only  one  boiler. 
Injectors  have  the  advantage  over  feed  pumps  that  they  util- 
ize practically  all  the  heat  supplied  to  them,  and  are  thus  very 
efficient  as  boiler  feeders;  they  deliver  hot  water  to  the  boiler; 
and  their  cost  is  small  when  compared  with  feed  pumps.  How- 
ever, they  have  the  disadvantage  that  they  cannot  handle 
water  at  a  temperature  above  160°  and,  if  they  have  to  lift 
their  supply  of  water,  they  cannot  handle  as  high  a  temperature 
as  this.  They  have  to  be  accurately  adjusted  for  the  steam 
pressure  to  be  used  and  they  are  sometimes  uncertain  in 
operation. 

The  action  of  an  injector  in  pumping  water  into  a  boiler  may 
be  illustrated  by  Fig.  151,  which  shows  the  necessary  parts  of  an 
injector.  Steam  from  the  boiler  enters  the  injector  at  A,  flows 
through  the  combining  tube  D  to  the  opening  0,  from  which  it 
passes  to  the  atmosphere  through  the  overflow  G.  As  the  steam 
flows  through  the  combining  tube  it  draws  air  out  of  the  suction 
pipe  B,  creating  a  partial  vacuum  in  it  and  causing  the  water  to 
rise  to  the  injector  and  come  in  contact  with  the  steam  at  the  end 
of  the  steam  nozzle  C.  The  steam  leaving  the  nozzle  C  has  a  high 
velocity  and,  as  it  is  condensed  by  contact  with  the  cold  water 
rising  through  B,  gives  enough  motion  to  the  water  to  raise  the 
check  valve  H  and  permit  it  to  pass  into  the  boiler.  As  soon  as 
water  begins  to  be  delivered  to  the  boiler,  steam  ceases  to  escape 
at  the  overflow  G. 


268 


STEAM  BOILERS 


Injectors  may  be  divided  into  two  general  classes — lifting  and 
non-lifting.     The  non-lifting  type  has  almost  dropped  out  of 


6TE.AM 


BOILER 


TO  BOILER 

FIG.  152. 


use,  and  is  not  of  enough  importance  to  consider  here.  In  order 
that  an  injector  be  able  to  lift  its  supply  of  water,  the  pressure 
at  the  end  of  the  steam  nozzle  must  be  less  than  that  of  the 


BOILER  ACCESSORIES  269 

atmosphere.  This  result  can  be  secured  by  properly  shaping 
the  steam  nozzle.  The  difference  between  these  two  classes  of 
injectors  is  therefore  entirely  in  the  shape  of  the  steam  nozzle. 

Lifting  injectors  may  be  again  divided  into  two  classes — auto- 
matic and  nonautomatic  injectors.  An  automatic  injector 
will  restart  automatically  if  its  operation  is  momentarily  inter- 
rupted, while  a  non-automatic  injector  must  be  restarted 
by  hand.  A  simple  form  of  non-automatic  lifting  injector  is 
shown  in  Fig.  152.  In  this  injector  the  steam  nozzle  is  provided 
with  a  conical  valve  for  regulating  the  flow  of  steam  at  starting. 
The  overflow  is  provided  with  a  check  valve  to  prevent  air 


FIG.  153. — Automatic  injector. 

entering  the  boiler  with  the  feed  water.  In  starting  this  injector, 
the  steam  valve  is  opened  slightly  until  water  flows  from  the 
overflow;  then  the  steam  valve  may  be  opened  wide  and  the 
water  will  be  forced  into  the  boiler. 

A  common  form  of  automatic  injector  is  shown  in  Fig.  153. 
The  features  which  make  this  injector  automatic  are  a  movable 
steam  nozzle  S  for  adjusting  the  opening  between  the  steam 
nozzel  and  the  combining  tube  V,  and  a  check  valve  R  for  clos- 
ing the  first  aperture  in  the  combining  tube.  This  injector 
works  on  the  same  principle  as  the  no n- automatic  type,  a 
partial  vacuum  being  created  in  the  suction  by  the  steam  draw- 
ing air  through  the  opening  between  the  steam  nozzle  S  and  the 
combining  tube  V.  At  starting,  the  steam  and  air  pass  into 
the  overflow  through  the  apertures  in  the  combining  tube  and 
through  the  check  valve  P.  As  soon  as  the  water  is  drawn  up 
to  the  end  of  the  steam  nozzel  it  condenses  the  steam  and  is 
forced  out  the  overflow.  If,  now,  the  steam  valve  is  opened 


270  STEAM  BOILERS 

wide,  the  energy  of  the  steam  will  carry  the  water  through 
the  tube  D  and  into  the  boiler.  When  water  begins  to  flow 
through  the  tubes  C  and  D  into  the  boiler,  a  suction  through 
the  two  openings  in  the  tube  C  is  created  which  closes  the  check 
valve  P  and  opens  the  flap  valve  R.  Should  the  flow  be  inter- 
rupted, the  valve  R  closes  and  the  starting  process  is  repeated 
automatically. 

The  injectors  described  up  to  this  point  are  all  of  the  single- 
tube  type.  An  injector  which  is  to  lift  water  through  a  con- 
siderable height  cannot  handle  very  hot  water,  because  different 


FIG.  154. — Hancock  inspirator. 

shaped  tubes  are  required  for  lifting  and  for  forcing  hot  water. 
Therefore,  in  order  for  an  injector  to  lift  and  to  feed  hot  water, 
it  must  have  two  tubes,  one  for  lifting  and  one  for  forcing,  thus 
making  it  a  double  injector.  An  injector  of  this  type,  known  as 
the  Hancock  Inspirator,  is  shown  in  Fig.  154.  In  operation, 
the  steam  valve  (140)  is  first  opened,  admitting  steam  to  the 
lifting  nozzle  (102).  The  action  of  this  nozzle  is  similar  to  that 
described  for  single-tube  injectors.  This  delivers  water  under 
a  slight  pressure  to  the  overflow  check  valve  (121).  Next, 
the  steam  valve  (146)  is  opened  and  water  is  forced  through  the 
main  combining  tube  (104)  and  into  the  boiler.  The  action  of 
opening  the  valve  (146),  closes  a  valve  in  the  overflow  (117  A), 
by  means  of  a  lever  connecting  it  with  the  main  lever  (137). 


CHAPTER  XVI 
CHIMNEYS  AND  DRAFT 

199.  Draft. — The  effectiveness  of  a  chimney  is  measured  by 
the  draft  which  it  can  produce.  The  draft  produced  by  a  chim- 
ney is  caused  by  the  difference  in  weight  of  the  air  inside  the 
chimney  and  that  outside.  The  air  inside  a  chimney  has  a 
higher  temperature  than  that  outside  and  is  lighter,  since 
warm  air  is  lighter  than  cold  air,  and  the  lighter  air  inside  the 
chimney  will  rise  and  cold  air  will  flow  in  to  take  its  place.  If 
the  cold  air  is  heated  as  it  enters  the  chimney,  the  draft  will  be 
continuous  and  there  will  be  a  current  of  air  flowing  in  the 
chimney.  That  is  what  happens  in  a  chimney  connected  to  a 
boiler;  the  air  is  heated  in  passing  through  the  furnace,  and  rises 
through  the  chimney,  while  cold  air  enters  to  take  its  place. 
Since  the  draft  in  a  chimney  is  produced  by  the  difference  in 
weight  between  the  column  of  air  inside  the  chimney  and  that 
outside,  the  draft  will  be  greater  with  a  high  temperature  inside 
the  chimney  or  with  a  tall  chimney.  In  other  words,  with  a 
given  temperature  outside  the  chimney,  the  draft  is  proportional 
to  the  temperature  inside  the  chimney  (measured  from  absolute 
zero)  and  to  the  height  of  the  chimney. 

The  draft  which  a  chimney  will  produce  may  be  found  by  the 
following  formula,  which  makes  an  allowance  of  20  per  cent  for 
friction  in  the  chimney: 


T     Tj 


in  which  D  is  the  draft  produced  by  the  chimney,  expressed  in 
inches  of  water. 

H  =  Height  of  top  of  chimney  above  grates,  in  feet 

P  =  Atmospheric  pressure  in  pounds  per  square  inch  (14.7  at 

sea  level) 
T  =  Atmospheric  temperature  expressed  in  absolute  degrees 

(Fahrenheit  plus  460) 
Tl=  Temperature  in  chimney,  expressed  in  absolute   degrees 

(Fahrenheit  plus  460°). 

271 


272  STEAM  BOILERS 

According  to  this  formula,  a  chimney  100  ft.  high  with  a  temper- 
ature inside  of  500°  F.  and  outside  of  60°  F.  would  have  a  draft, 
at  sea  level,  of 


(±-  ± 

\520     960 


L7 
=  about  .54  in.  of  water. 

By  Inches  of  Water  is  meant  that  the  draft  is  strong  enough  to 
support  a  column  of  water  that  many  inches  high.  Thus,  in 
the  example  just  given,  the  draft  pulls  with  a  force  strong 
enough  to  support  a  column  of  water  .54  in.  high.  If  the  draft 
were  applied  to  one  end  of  a  U-tube  containing  water,  this  water 
would  stand  .54  in.  higher  in  one  side  of  the  tube  than  in  the 
other. 

The  draft  produced  by  a  chimney  is  not  all  available  for 
drawing  air  through  the  fire,  which  is  its  most  important  office, 
for  it  must  also  overcome  the  friction  of  the  chimney,  the  breech- 
ing or  connection  between  the  chimney  and  boiler,  the  resistance 
of  the  boiler  passes,  and  the  resistance  of  the  fire  itself.  After 
these  things  are  provided  for,  there  must  be  enough  draft  left  to 
keep  the  fires  burning  properly.  The  above  formula  allows  20 
per  cent  of  the  draft  for  overcoming  the  friction  of  the  chimney, 
which  seems  to  be  a  fair  average  value.  The  loss  of  draft  in 
the  breeching  may  be  estimated  as  .1  of  an  inch  of  water  for 
each  100  ft.  length,  with  an  additional  loss  of  .05  of  an  inch  for 
each  right  angle  bend,  and  the  loss  in  the  boiler  passes  will 
vary  from  .3  to  .6  of  an  inch,  depending  on  the  kind  of  boiler. 

The  draft  necessary  to  force  air  through  the  fire  will  depend 
upon  the  kind  of  coal  burned,  upon  the  thickness  of  the  fire, 
and  upon  the  rate  at  which  the  coal  is  being  burned,  there- 
fore it  varies  through  a  wide  range.  A  coal  that  packs  closely 
on  the  grate  will  require  more  draft  to  force  air  through  it  than 
a  more  open  grade  of  coal;  also,  the  thicker  the  fire,  the  more 
draft  will  be  required,  and  a  high  rate  of  combustion  requires 
more  air  and  therefore  a  stronger  draft  than  does  a  low  rate  of 
combustion.  The  curves  shown  in  Fig.  155  give  the  amount 
of  draft  required  for  different  kinds  of  fuels  when  burned  at 
different  rates  of  combustion  and  with  the  thickness  of  fire 
ordinarily  used  in  practice.  These  curves  were  originated  by 
the  Stirling  Company  from  results  of  a  large  number  of  tests. 

To  illustrate  the  method  of  determining  the  amount  of  draft 


CHIMNEYS  AND  DRAFT 


273 


required,  suppose  we  have  a  boiler  which  burns  20  Ib.  of  bitu- 
minous run  of  mine  per  square  foot  of  grate  surface  per  hour,  the 
breeching  being  50  ft.  long  with  two  right-angled  bends.  The 
draft  required  will  be 


1.40 


5  10  15  20  25  30  35  40  45 

Pounds  of  Coal  Burned  per  Square  Toot  of  Grate  Surface  per  Hour 

FIG.  155. 

For  the  breeching 5  X  .1  =  .05  in.  of  water 

For  two  bends  in  breeching 2  X  .05  =  .10 

For  the  fuel  (from  curve) .10 

For  the  boiler  passes  (average  assumed) . .  .45 

Total .70  in.  of  water 

Assuming  a  temperature  of  90°  F.  in  the  boiler  room  and  of  500° 
F.  in  the  chimney,  the  height  of  the  chimney  may  be  found 
from  the  formula 


-42  77  VP( 

—  .^s  n  x.r\  ^p—  7^ 


1 


70  —  49 

'"460+90  460  +  500 

.70  =  6.174  /fx. 000776  =  .00479  H 
.70 


.00479 


=  146  ft. 


Shorter  methods  than  the  above  have  been  used  quite  com- 
monly for  determining  the  height  of  chimney  necessary,  such 


274  STEAM  BOILERS 

shorter  formulas  usually  being  derived  from  experience.  The 
following  short  formula  for  finding  the  height  of  chimney  is 
suggested  as  giving  very  good  results  : 

180C2 
H=  ~T 

in  which  H  is  the  height  of  chimney  in  feet 

t  is  the  temperature  of  gases  inside  the  chimney 
and       C  is  the  pounds  of  fuel  burned  per  square  foot  of  grate 

surface  per  hour. 

Applying  this  formula  to  the  above  example,  the  height  of 
chimney  should  be 

180X202 


500 


The  volume  of  gases  handled  by  a  chimney  depends  on  the 
area  of  cross-section  of  the  chimney.  It  also  depends  on  the 
height  of  the  chimney,  since  a  tall  chimney  will  move  the  gases 
faster  than  a  short  one.  The  volume  of  gases  to  be  handled 
depends  on  the  amount  of  coal  burned.  The  relation  of  these 
quantities  can  be  reduced  to  the  following  simple  formula: 

A-  -*- 

12VH 

in  which  A  is  the  area  of  cross-section  of  the  top  of  chimney,  in 

square  feet. 

H  is  the  height  of  the  chimney  in  feet  and 
F  is  the  number  of  pounds  of  coal  burned  per  hour. 

If,  in  the  problem  given  above,  the  boiler  had  60  sq.  ft.  of  grate 

surface,  the  total  coal  burned  per  hour  would  be  60X20  =  1200 

lb.,  and  the  area  of  the  chimney  should  be 


which  would  give  a  diameter  of 


">/ 


=  ^10:54  =  3.25  ft.  or  3  ft.  3  in. 


For  square  chimneys,  the  corners  should  be  neglected,  and  the 
area  taken  as  that  of  a  circle  which  would  fit  inside  the  chimney. 
Thus  if  a  square  chimney  was  used  with  the  above  boiler,  the 
chimney  should  be  3  ft.  3  in.  square  on  the  inside. 


CHIMNEYS  AND  DRAFT  275 

If  the  horse-power  of  the  boilers  and  the  rate  of  combustion 
are  known,  the  same  formulas  may  be  used  to  determine  the  size 
of  chimney  required.  Thus,  suppose  the  height  of  chimney  in 
order  to  provide  enough  draft,  is  to  be  146  feet,  as  before,  and 
we  wish  to  find  the  diameter  of  a  round  chimney  which  will  be 
large  enough  for  1000  h.p.  of  boilers  which  are  of  such  type 
that  4  pounds  of  coal  will  be  burned  per  horse-power. 

1000  h.p.  will  require  the  burning  of  1000X4=4000  Ib.  of 
coal  per  hour.  Therefore  the  area  of  the  chimney  would  be 


and  its  diameter  would  be 


D=    l27^  =  v/35. 14=5.93  or  about  5  ft.  11  in. 

\  .  I  OO4: 

The  area  of  the  breeching  should  be  about  20  per  cent  greater 
than  the  area  of  the  chimney  as  calculated  above.  Thus,  the 
breeching  for  the  example  which  we  have  just  worked  would 
have  an  area  of  1.20x27.6=33.12  sq.  ft. 

If  there  are  a  number  of  boilers,  the  size  of  the  breeching 
would  be  reduced  from  each  boiler  to  the  next  Thus,  if  there 
are  two  500=  h.p.  boilers  in  the  problem  which  we  have  just 
worked,  the  breeching  would  have  an  area  of  34.2  sq.  ft.  between 
the  chimney  and  the  first  boiler,  and  an  area  of  33. 12 -=-2  =  16. 56 
sq.  ft.  between  the  first  boiler  and  the  second.  In  all  cases  the 
breeching  should  be  covered  with  a  non-conducting  material,  to 
prevent  a  reduction  in  temperature  of  the  gases  before  reaching 
the  chimney. 

200.  Chimneys  for  Oil  Fuel. — Chimneys  for  boilers  which  use 
oil  fuel  need  be  only  about  90  ft.  high  and  with  a  cross-sectional 
area  about  one-half  as  great  as  if  bituminous  coal  were  to  be 
used.     However,  they  are  usually  built  as  though  bituminous 
coal  were  to  be  used  for  fuel.     Then,  if  oil  is  abandoned  as  a  fuel, 
it  is  not  very  expensive  to  change  over  to  coal. 

201.  Steel   Chimneys. — The   materials   most   commonly  used 
in   chimney   construction   are   steel,    reinforced   concrete,    and 
brick. 

Steel  chimneys  are  being  used  very  commonly  as  they  have 
many  advantages.  Among  these  are,  low  cost  as  compared 
with  other  kinds,  small  space  occupied,  since  they  are  not  so 

23 


276 


STEAM  BOILERS 


V(g 


Half  Section 


thick,  great  strength  for  a  given  weight,  less  ex- 
pensive foundation  required,  and  great  effici- 
ency provided  the  plates  are  caulked  after  being 
riveted  together,  thus  making  them  practically 
air-tight.  Air  leaking  into  a  chimney  reduces 
the  draft  and  therefore  makes  it  less  efficient. 
Against  these  advantages  are  its  higher  cost  of 
maintenance  as  it  must  be  painted  frequently 
to  prevent  its  rusting.  Unless  properly  lined,  a 
steel  chimney  may  be  attacked  by  the  sulphur 
fumes  in  the  smoke,  which  eat  away  the  steel 
and  weaken  the  chimney. 

Steel  chimneys  are  usually  placed  upon  a 
cast-iron  or  steel  plate  which  rests  upon  a  con- 
crete foundation.  If  a  cast-iron  plate  is  used, 
its  thickness  should  not  be  less  than  1  in. 

Steel  chimneys  may  be  sustained  by  guy  wires 
or  be  self-sustaining.  Four  guy  wires  placed  90 
degrees  apart  around  the  chimney  are  used  in 
each  set.  If  one  set  of  wires  is  used,  they  should 
be  placed  at  two-thirds  the  height  of  the  chim- 
ney, and  if  two  sets  are  used,  the  lower  ones 
should  be  placed  at  one-third  the  height.  All 
guy  wires  should  be  anchored  at  a  distance  from 
the  base  of  the  stack  equal  to  the  height  at 
which  they  are  attached  to  the  chimney. 

Steel  chimneys  are  made  self-sustaining  by 
flaring  the  bottom  part  to  about  twice  the  dia- 
meter of  the  upper  part,  and  bolting  it  securely 
to  a  steel  or  cast-iron  base  plate,  which  is 
bolted  directly  to  the  foundation.  A  chim- 
ney of  this  kind 
is  shown  in  Fig. 
156.  These 
chimneys  are 
usually  lined 
with  a  second 
quality  of  fire 
brick  for  a 
height  of  about 
50  ft.  from  the 


30'-  O"-^ 

Half  Elevation  P|an 

FIG.  156.— Steel  chimney. 


CHIMNEYS  AND  DRAFT  277 

bottom,  and  above  this  with  well  burned  red  brick,  if  they  are 
lined  at  all.  It  is  better  to  line  them,  as  this  protects  the 
metal  from  the  sulphur  fumes  mentioned  above.  The  lining 
should  have  a  thickness  of  not  less  than  4J  in.  at  the  top  and 
increase  in  thickness  4J  in.  for  about  every  30  ft.  In  any  case 
the  lining  need  be  only  thick  enough  to  be  self  sustaining. 

202.  Concrete    Chimneys. — Chimneys   built    of    concrete,    re- 
inforced with  steel  rods,  have  been  used  to  some  extent  in  recent 
years  and  are  proving  very  satisfactory.     These  chimneys  are 
built  of  a  thin  wall  of  concrete  having  vertical  steel  rods  placed 
near  the  outer  wall  and  with  steel  rings  placed  horizontally,  the 
rings  having  a  diameter  slightly  less  than  the  outside  diameter 
of  the  chimney.     Constructed  in  this  way,  a  concrete  chimney 
is  very  strong  and  yet  weighs  only  about  one-third  as  much 
as   a  brick    chimney   of    equal    capacity.     Besides    these   ad- 
vantages, it   does   not  leak   air,  is   very  durable,  costs   prac- 
tically nothing  to  keep  in  repair,  and  occupies  less  space  than 
a  brick  chimney.     It  is  also  much  less  expensive  to  build  than 
a  brick  chimney  and  can  be  constructed  faster. 

203.  Brick  Chimneys. — Most    of   the   power-plant    chimneys 
erected  in  the  past  have  been  built  of  brick,  but  this  material 
is  being  largely  replaced  by  steel,  or  steel  and  concrete  combined. 
Brick  chimneys  are  built  round,  octagonal,  or  square,  the  round 
ones  having  the  best  shape  to  produce  draft  and  weighing  less 
in  proportion  to  their  size,  but  the  square  ones  costing  less  to 
build.     Nearly  all  brick  chimneys  are  built  with  a  lining  which 
extends  either  the  entire  height  of  the  chimney  or  to  a  point 
about  50  ft.  from  the  ground.     The  lining  should  be  built  inde- 
pendent of  the  outside  of  the  chimney  so  it  will  not  be  injured  by 
expansion  and  contraction  of  the  outer  walls,  and  so  it  may 
be  repaired  or  replaced  without  tearing  down  the  outer  walls. 
The  lining  may  be  of  hard  burned  common  brick,  though  fire 
brick  is  better  suited  to  this  purpose.     In  some  cases,  where  the 
chimney  is  built  of  good  hard  burned  common  brick,  it  is  not 
lined  at  all,  but  such  chimneys  are  apt  to  develop  cracks  due  to 
changes  of  temperature,  and  therefore  leak  air,  which  lessens 
the  draft.     A  good  example  of  brick  chimney  construction  is 
shown  in  Fig.  157. 

Round  chimneys  are  often  built  of  radial  brick,  similar  to 
those  shown  in  Fig.  158.  These  brick,  which  have  square  holes 
through  them,  are  larger  than  ordinary  brick  and  are  molded 


278 


STEAM  BOILERS 


ELEVATION 
FIG.  157. — Brick  chimney. 


CHIMNEYS  AND  DRAFT 


279 


to  fit  into  a  certain  place  in  the  chimney.  Their  shape  permits 
their  being  laid  with  thinner  joints  and,  being  of  large  size,  the 
joints  are  not  so  numerous.  The  holes  through  the  bricks 
do  not  allow  the  heat  to  pass  through  them  so  readily  after 
they  are  placed  in  the  chimney  and  they  make  a  lighter 
chimney  than  if  they  were  solid. 


FIG.  158. — Radial  brick.  '  * 

204.  Artificial  Draft. — Besides  natural  draft,  or  that  created 
by  a  chimney,  there  are  two  common  methods  of  producing 
draft  by  artificial  means.  These  methods  are  (1)  by  means  of 
steam  jets,  and  (2)  by  means  of  fans,  or  mechanical  draft,  as 
it  is  commonly  called. 


FIG.  159. 

205.  Steam  Jets. — Fig.  159  illustrates  one  method  of  producing 
draft  by  means  of  steam  jets  In  this  method,  the  draft  is  pro- 
duced by  a  jet  of  steam  which  discharges  beneath  the  grates, 
forcing  the  air  and  steam  up  through  the  grates  and  fuel  bed. 


280  STEAM  BOILERS 

The  jet  is  produced  by  a  hollow  ring  with  small  holes  of  1/16  to 
1/8  in.  in  diameter  bored  in  its  side,  the  ring  being  connected 
directly  to  the  steam  space  of  the  boiler  instead  of  to  the  main 
steam  pipe,  so  it  may  be  operated  at  times  when  steam  is  not 
being  taken  from  the  boiler.  All  the  small  jets  discharge  in 
the  same  direction  into  a  nozzle  placed  just  below  the  level  of 
the  grates,  and  serve  to  draw  air  through  the  center  of  the  ring 
and  the  nozzle,  discharging  it  into  the  ash  pit  under  the  grates. 

The  same  form  of  steam  jet  described  above  is  sometimes 
placed  in  the  base  of  the  chimney  and  directed  upward  in  order 
to  produce  a  draft  by  drawing  air  through  the  nozzle.  Unless 
large  quantities  of  steam  are  used,  the  draft  produced  by  this 
method  will  be  small.  The  draft  in  a  locomotive  boiler  is  pro- 
duced by  this  method,  but  in  this  case  all  the  steam  exhausted 
from  the  engine  cylinders  passes  through  the  nozzles  and  pro- 
duces a  very  powerful  draft,  often  amounting  to  from  3  to  8  in. 
of  water.  In  a  locomotive  boiler,  the  steam  used  in  the  draft 
nozzles  does  not  represent  a  loss,  as  in  stationary  work,  because 
the  steam  first  does  work  in  the  engine  cylinders  and,  if  it  were 
not  used  in  the  nozzles,  would  be  wasted.  Since  the  amount  of 
steam  passing  through  the  nozzles,  and  therefore  the  draft, 
depends  on  the  amount  of  work  the  engines  are  doing,  the 
device  is  self-regulating. 

Steam  jets  are  sometimes  placed  in  the  bridge  wall  and  di- 
rected toward  the  front  of  the  furnace,  or  placed  along  the  sides 
of  the  furnace  and  directed  toward  the  center.  In  these  posi- 
tions, however,  they  serve  simply  to  mix  the  air  and  gases  more 
thoroughly,  and  thereby  promote  more  complete  combustion 
but  do  not  increase  the  draft  to  an  appreciable  extent. 

It  may  be  said  in  favor  of  steam  jets  for  producing  draft  that 
they  are  cheap  to  install  and  are  convenient  for  taking  care  of 
sudden  and  very  large  overloads.  They  are  very  wasteful  of 
steam,  using  from  5  to  21  per  cent  of  the  total  steam  generated 
by  the  boiler  and,  in  addition  to  the  loss  from  this  source,  steam 
admitted  through  the  grates  must  be  heated  to  the  temperature 
of  the  flue  gases,  and  the  heat  required  to  do  this  is  wasted. 
Steam  jets  beneath  the  grates  help  to  prevent  clinkers  from 
adhering  to  the  grates,  and,  with  certain  varieties  of  coal,  this 
may  be  an  important  feature,  though  it  would  not  justify  the 
waste  of  steam  caused  by  running  the  steam  jet  all  the  time. 

206.  Mechanical  Draft. — Under  certain  conditions,  draft  pro- 


CHIMNEYS  AND  DRAFT 


281 


duced  by  a  fan,  or  mechanical  draft,  has  many  advantages  over 
the  method  of  producing  it  by  a  chimney,  and  in  some  cases 
such  as  the  production  of  draft  for  the  boilers  of  a  war  vessel 
where  a  high  rate  of  combustion  must  be  secured  and  where 
the  height  of  the  chimney  or  funnel  is  limited,  the  fan  has  so 
many  advantages  as  compared  to  other  methods  of  producing 
draft  that  its  use  for  this  purpose  is  almost  absolutely  necessary. 
207.  Forced  Draft. — There  are  two  common  ways  of  using 
a  fan  to  produce  draft,  called  the  forced  draft  system  and  the 
induced  draft  system.  In  the  forced  draft  system  the  air  pressure 
beneath  the  grate  is  greater  than  that  of  the  atmosphere  and 
the  air  is  forced  up  through  the  bed  of  fuel.  The  air  may  be 
supplied  under  pressure  either  by  closing  the  firing  room  or 
stoke  hole  air-tight  and  forcing  the  air  into  it  under  slight  pres- 
sure, or  by  closing  the  ash  pit  air-tight  and  discharging  the  air 
into  it  under  a  slight  pressure.  In  the  first,  or  closed  stoke-hole 
system,  the  air  gradually  escapes  into  the  ash  pits  under  the 
boilers  and  then  up  through  the  grates  and  fuel  bed  and  out' 
through  a  chimney,  which  needs  to  be  only  tall  enough  to  carry 


FIG.  160. — Closed  ash  pit  systems  of  forced  draft. 

the  gases  out  of  the  way.  Ample  ventilation  is  provided  for 
the  fireman  by  this  method,  as  the  fan  discharges  a  large  quantity 
of  fresh  air  into  the  firing  room.  This  method  is  well  suited  to 
war  vessels,  where  the  firing  room  can  readily  be  made  air-tight, 
and  it  has  been  widely  adopted  by  the  United  States  Navy. 

The  closed  stoke-hole  system  is  not  well  suited  to  stationary 
plants  on  account  of  the  difficulty  of  constructing  the  firing  room 
tight  enough  to  prevent  the  loss  of  large  quantities  of  air  by 
leakage.  For  this  kind  of  power  plant  the  closed  'ash-pit  system 
has  come  into  common  use.  Fig.  160  illustrates  one  method  of 
applying  this  system  to  a  battery  of  boilers.  The  fan,  which 


282  STEAM  BOILERS 

is  driven  by  a  small  steam  engine,  is  set  at  one  side  of  the  battery 
of  boilers  and  discharges  downward  into  a  duct  built  under  the 
floor  and  running  under  the  fronts  of  the  boilers,  a  branch 
leading  into  each  ash  pit,  which  is  kept  tightly  closed.  An 
objection  to  this  method  of  construction  is  that  cinders  may 
fall  into  the  air  inlets  and  gradually  choke  up  the  duct.  A 
better  construction  is  to  run  the  duct  beneath  the  bridge  walls 
of  the  boiler  and  place  the  inlet  to  the  ash  pit  in  the  front  of 
the  bridge  wall,  as  shown  in  Fig.  161. 

In  both  of  the  constructions  described  above,  the  air  supply 
to  each  boiler  must  be  equipped  with  a  damper  for  shutting  it 


FIG.  161. 

off  when  the  furnace  door  is  to  be  opened.  Unless  this  damper 
is  closed  when  the  furnace  door  is  opened  the  flame  and  smoke 
will  be  blown  outward  and  there  is  danger  of  the  fireman  being 
burned. 

208.  Induced  Draft. — In  the  induced  draft  system,  a  fan  is 
connected  in  the  breeching  in  such  manner  as  to  suck  or  draw 
air  through  the  furnace.  Fig.  162  shows  the  general  construc- 
tion of  an  induced  draft  system.  The  fan  is  usually  placed 
about  on  a  level  with  the  tops  of  the  boilers,  so  the  breeching 
can  lead  directly  into  the  center  of  the  fan  casing.  The  furnace 
gases  enter  the  fan  at  its  center  and  are  discharged  from  its 
circumference  directly  into  a  short  stack.  The  breeching  is 
usually  provided  with  a  by-pass  for  leading  the  gases  around  the 
fan  and  directly  into  the  stack  in  case  of  an  accident  to  the  fan. 
Dampers  are  provided  for  shutting  off  the  gases  from  the  fan 
and  for  opening  the  by-pass.  In  many  installations,  two  fans, 


CHIMNEYS  AND  DRAFT 


283 


each  with  capacity  enough  to  handle  all  the  gases,  are  installed 
so  that  in  case  of  accident  to  one  the  other  may  be  used,  each 
fan  being  used  on  alternate  days  or  alternate  weeks  to  keep 
both  of  them  in  good  working  order. 

With  the  induced  draft  system,  the  pressure  of  the  air  inside 
the  furnace  and  ash  pit  is  always  less  than  that  of  the  atmos- 
phere. Therefore  it  is  not  necessary  to  shut  off  the  draft  when 
cleaning  the  fires  or  ash  pit,  or  when  firing,  and  the  fire  burns 
more  evenly  over  the  entire  grate  and  requires  less  attention 
than  with  forced  draft.  On  the  other  hand,  an  induced  system 
costs  more  than  a  forced  draft  system  on  account  of  its  requiring 
a  larger  fan.  A  larger  fan  is  required  with  an  induced  draft 
system  because  it  handles  warm  air,  while  in  a  forced  draft 


FIG.  162. — Induced  draft  system. 

system,  the  fan  handles  comparatively  cool  air,  which  there- 
fore occupies  less  volume;  but  it  does  not  require  as  much  power 
to  move  a  cubic  foot  of  warm  air  as  it  does  to  move  a  cubic  foot 
of  cold  air,  since  the  density  of  the  warm  air  is  less.  Therefore, 
while  the  size  of  fan  for  an  induced  draft  system  is  about  twice 
that  for  forced  draft  for  the  same  plant,  it  does  not  require 
twice  as  much  power  to  run  it. 

Local  conditions  will  usually  determine  whether  it  is  better 
to  use  chimney  or  mechanical  draft.  A  few  street  railway  and 
lighting  plants  are  provided  with  both  chimney  and  fans,  the 
fans  being  used  when  the  heaviest  load  is  carried,  and  the 
chimney  alone  used  for  ordinary  loads. 

Mechanical  draft  offers  many  advantages  over  natural  or 
chimney  drafts,  especially  with  low-grade  fuel.  Since  the 

24 


284  STEAM  BOILERS 

amount  of  draft  produced  by  a  chimney  depends  upon  its 
height  and  the  temperature  in  it,  its  first  cost  becomes  very 
great  if  a  low  grade  of  fuel  is  used  which  requires  a  strong  draft. 
The  first  cost  of  a  fan  system  will  usually  be  much  less  than  that 
of  an  equivalent  chimney.  With  a  fan  system  a  very  strong 
draft  can  be  carried  and,  with  it,  a  thick  fire,  which  promotes 
complete  combustion  and  requires  less  air  per  pound  of  fuel 
burned.  The  speed  of  a  fan  can  be  quickly  changed  to  suit  the 
load  on  the  boilers  and  it  can  be  speeded  up  to  furnish  enough 
draft  for  large  overloads.  Damp  weather  affects  the  draft  of  a 
chimney  but  makes  no  change  in  the  draft  produced  by  a  fan. 

One  of  the  principal  objections  urged  against  mechanical 
draft  is  the  cost  of  the  power  to  run  the  fan.  A  fan  requires 
from  1J  to  5  per  cent  of  the  steaming  capacity  of  the  boilers 
to  run  it,  depending  upon  the  kind  of  engine  used  and  the  con- 
ditions under  which  it  is  operated.  The  cost  of  operation  of  the 
fan  may  be  reduced  if  the  exhaust  from  the  fan  engine  can  be 
used  for  heating  the  building  or  for  heating  the  air  supply  of  the 
furnaces. 

209.  Economizers  and  Air  Heaters. — With  either  natural  or 
mechanical  draft  the  temperature  of  the  waste  gases  will  be  about 
500°  F.  A  simple  calculation  will  show  the  large  loss  resulting 
from  this  high  temperature.  Suppose  24  Ib.  of  air  are  admitted 
to  the  furnace  for  each  pound  of  combustible  burned,  the  tem- 
perature in  the  boiler  room  being  90°  and  the  temperature  of  the 
waste  gases  being  500°  F.  The  specific  heat  of  the  waste  gases 
will  be  about  .25.  For  each  pound  of  combustible  burned  there 
will  be  24  +  1=25  Ib.  of  hot  gases  passing  out  the  chimney, 
which  will  carry  away  and  waste 

.25X25X(500-90)  -2562   B-.t.u., 

representing  a  larger  per  cent  of  the  heat  in  the  fuel. 

If  the  draft  is  produced  by  a  chimney,  and  an  attempt  is 
made  to  reduce  this  loss  by  lowering  the  temperature  of  the 
gases,  the  draft  will  be  reduced,  since  the  amount  of  draft  depends 
upon  the  temperature  in  the  chimney  as  well  as  upon  its  height. 
Therefore,  unless  the  chimney  is  much  too  large  for  the  plant 
it  is  serving,  it  will  not  be  practicable  to  reduce  the  temperature 
of  the  waste  gases. 

If  the  draft  is  being  produced  by  a  fan,  the  above  high  tem- 
peratures are  not  necessary  and  may  be  reduced  without  affect- 


CHIMNEYS  AND  DRAFT  285 

ing  the  draft.  A  method  commonly  used  for  saving  a  part  of 
the  heat  which  would  otherwise  be  lost  is  by  the  use  of  an 
economizer. 

An  economizer  is  a  feed-water  heater  which  is  placed  in  the 
flue  leading  from  the  boiler  to  the  chimney  and  is  heated  by 
the  hot  flue,  gases.  Economizers  are  usually  made  up  of  a  num- 
ber of  4-in.  pipes  placed  in  a  vertical  position  and  connected 
at  the  top  and  bottom  by  headers.  Cold  water  enters  the  pipes 
at  one  end  of  the  enconomizer  and  the  hot  gases  passing  between 
the  pipes  heat  the  water.  As  the  flue  gases  usually  have  a 


FIG.  163. — Economizer  connected  to  boiler. 

temperature  of -from  450°  to  500°  the  feed  water  may  be  heated 
to  the  boiling-point,  but  in  order  to  do  this  the  water  must  be 
under  pressure  and  the  heater  closed,  otherwise  steam  would 
be  generated.  The  heat  utilized  by  an  economizer  is  heat  that 
would  otherwise  be  wasted  and,  therefore,  whatever  heat  is 
given  to  the  feed  water  by  it  represents  a  direct  saving,  and  the 
amount  of  this  saving  is  considerable.  Economizers  are  com- 
monly used  with  mechanical  draft  systems,  in  which  case  they 
are  placed  directly  in  the  breeching  between  the  boiler  and 


286  STEAM  BOILERS 

chimney,  as  shown  in  Fig.  163.  The  economizer  is  usually  set 
in  such  manner  that  the  gases  may  be  by-passed  around  it  in 
case  it  is  shut  down  for  repairs.  When  induced  draft  is  used, 
the  fan  is  usually  placed  so  as  to  draw  the  gases  through  the 
economizer,  but  with  forced  draft,  of  course,  the  fan  blows 
through  furnace,  boiler,  and  economizer. 

The  principal  objection  to  economizers  comes  from  the  difficulty 
of  keeping  the  tubes  clear,  both  inside  and  outside,  and  from 
the  difficulty  of  preventing  leakage,  brought  about  by  excessive 
expansion  of  the  economizer  due  to  the  high  temperature  to 
which  they  are  subjected.  If  soot  is  allowed  to  remain  on  the 
tubes,  it  retains  moisture  and  seems  to  have  an  acid  action  on 
the  tubes,  gradually  corroding  them.  As  the  water  in  an 
economizer  is  subjected  to  a  high  temperature,  impurities  will 
•be  deposited  in  it  from  impure  water,  and  it  is  necessary  to  clean 
the  tubes  on  the  inside  to  keep  them  working  efficiently.  For 
this  purpose  handholes  through  which  they  may  be  cleaned 
are  placed  over  each  tube. 

It  often  happens  that  there  will  still  be  an  excess  of  heat  in 
the  flue  gases,  even  after  passing  through  the  economizer  and 
heating  the  feed  water.  This  heat,  which  would  otherwise 
be  wasted,  may  be  used  to  heat  the  air  which  is  fed  into  the 
furnaces,  by  providing  a  device  built  like  an  econo.mizer,  but 
arranged  to  pass  air  instead  of  water  though  the  pipes.  Cold 
air  admitted  to  a  furnace  chills  the  fire  by  taking  some  of  the 
heat  to  raise  its  temperature,  hence  there  is  an  advantage  in 
using  warm  air  if  it  can  be  readily  obtained. 


CHAPTER  XVII 
BOILER  FEED  WATERS 

210.  Scale.  —  The  waters  of  our  lakes,  rivers,  springs,  and 
underground  streams  contain  more  or  less  mineral  substances 
that  have  been  dissolved  by  the  water  in  its  passage  through  the 
earth,  and  also  more  or  less  dirt,  mud,  and  vegetable  matter 
which  have  been  taken  up  and  carried  along  by  the  water.  When 
water  is  evaporated  in  a  boiler,  all  of  these  impurities  are  left 
behind  and  are  usually  deposited  in  solid  form.  In  some  cases 


Scale  H,  Thick,    5%  Additional  Fuel  required. 


these  substances  merely  settle  as  a  soft  mud  and  can  be  blown  off, 
but  more  often  they  form  a  hard  scale  on  all  the  heating  sur- 
face, which  is  difficult  to  remove.  The  scale  thus  formed  is  a 
very  poor  conductor  of  heat  and  its  presence,  therefore,  reduces 
the  efficiency  and  capacity  of  a  boiler  by  reducing  the  amount 
of  heat  that  can  pass  through  the  heating  surface.  Fig.  164 
shows  how  great  may  be  the  effect  of  a  small  amount  of  scale. 
In  the  case  of  water-tube  boilers,  scale  collecting  in  the  tubes 
greatly  hinders  the  circulation  of  water  and  liberation  of  steam. 
Besides  increasing  the  coal  bills,  scale  causes  the  boiler  to  wear 
rapidly.  Due  to  the  presence  of  the  scale,  heat  cannot  pass 
through  the  metal  readily  and  be  taken  up  by  the  water,  hence, 
the  metal  becomes  overheated  from  the  storage  of  heat  in  it, 
and  may  be  burned  or  it  may  even  reach  a  temperature  at 
which  it  will  bag  or  burst,  due  to  the  pressure  within  the  boiler. 
Some  forms  of  scale  contain  certain  acids  which  may  attack 
the  iron  and  corrode  or  eat  it  away. 
25  287 


288  STEAM  BOILERS 

It  is  much  better,  as  far  as  possible,  to  prevent  the  scale-form- 
ing substances  from  entering  the  boiler,  as,  once  inside,  they 
will  form  a  more  or  less  hard  scale  which  must  be  removed. 
Even  though  the  scale  formed  is  soft  and  easily  removed,  its 
presence  involves  a  certain  expense  in  laying  off  the  boiler  and 
cleaning  it.  To  prevent  the  formation  of  scale,  requires  a  knowl- 
edge of  the  chemistry  of  feed  water  and  of  the  proper  treatment 
by  which  the  mineral  salts  may  be  removed  before  feeding  the 
water  into  the  boiler,  or  they  may  be  changed  in  nature  so  they 
will  not  form  a  hard  scale  but  will  settle  as  a  soft  scale  or  as 
mud  which  can  be  blown  off  or  easily  removed. 

211.  Impurities  in  Feed  Waters. — Practically  all  waters  avail- 
able for  boiler  feeding   contain  some  impurities.     The  effects 
of  these  impurities   vary    considerably   but    they   are    always 
injurious. 

The  impurities  most  often  found,  and  found  in  the  largest 
quantities,  are  given  below  together  with  their  chemical  formulae : 

Calcium  carbonate CaCO3 

Magnesium  carbonate MgCO3 

Calcium  sulphate CaSO4 

Magnesium  sulphate MgSO4 

The  impurities  less  frequently  found  and  in  smaller  quantities 
are: 

Iron  carbonate Fe2CO3 

Magnesium  chloride MgCl2 

Calcium  chloride CaCl2 

Potassium  chloride KC1 

Sodium  chloride NaCl 

Besides  these  there  maybe  some  iron  oxides,  calcium  phosphate, 
silica,  and  organic  matter,  which  usually  occur  in  very  small 
quantities. 

212.  The    Carbonates. — Calcium    carbonate    and   magnesium 
carbonate  do  not  dissolve  very  readily  in  pure  water,  but  most 
water  contains  some  carbonic  acid  (CO2)  and  if  this  is  present, 
the   carbonates   dissolve   very  readily.     The   carbonates   unite 
with  the  carbonic  acid  and  form  the  bicarbonates  of  calcium  and 
magnesium,    which    are  very  soluble.     This    combination   can, 
however,  be  broken  up  by  heating,  which  drives  off  the  carbonic 
acid  gas  and  returns  the  carbonates  to  the  insoluble  form,  when 
they  will  be  deposited.     The  action  described  above,  begins  when 


BOILER  FEED  WATERS  289 

the  water  is  heated  to  180°  F.  and  by  the  time  it  has  reached 
212°  F.,  the  greater  part  of  the  carbonates  will  be  deposited.  It 
requires  a  temperature  of  about  290°  F.  to  deposit  all  of  the 
carbonates,  but  the  larger  part  is  deposited  between  the  tem- 
peratures of  180°  and  212°  F. 

If  the  feed  water  enters  the  boiler  at  a  temperature  lower 
than  180°  F.  the  carbonates  will  be  deposited  inside  the  boiler 
but,  if  some  device  is  used  whereby  the  feed  water  is  heated  to 
a  temperature  of  about  210°  or  212°  before  it  enters  the  boiler, 
there  will  be  very  little  of  the  carbonates  deposited  in  it  and  it 
will  be  easily  cleaned.  As  exhaust  steam  has  a  temperature  of 
at  least  212°,  it  may  be  used  to  heat  the  feed  water  to  a  high 
enough  temperature  to  deposit  most  of  the  carbonates.  Such 
a  feed-water  heater  should  have  enough  storage  capacity  to 
allow  the  water  to  remain  in  it  some  time,  as  the  carbonates 
settle  slowly. 

Calcium  carbonate  and  magnesium  carbonate  form  a  porous 
deposit  which  does  not  adhere  closely  to  the  metal;  therefore, 
they  are  not  particularly  troublesome  in  themselves,  but  often 
there  is  some  other  substance  present  which  mixes  with  the 
deposit  and  cements  it  into  a  hard  scale.  Magnesium  carbonate 
sometimes  breaks  up,  forming  magnesium  hydrate,  which  is  a 
very  active  cement.  This  is  usually  present  in  sufficient  quan- 
tities to  bind  the  carbonates  into  a  scale,  even  though  there 
is  an  absence  of  other  cementing  substances.  If  there  are  no 
cementing  substances  present,  the  carbonates  form  a  scale  which 
is  not  difficult  to  remove. 

213.  The  Sulphates. — Calcium  sulphate  and  magnesium  sul- 
phate are  the  most  troublesome  impurities,  as  they  form  an  ex- 
ceedingly hard  scale  which  is  difficult  to  remove.  The  sulphates 
remain  in  solution  until  a  temperature  of  about  300°  is  reached, 
when  they  become  insoluble  and  settle.  Since  they  remain 
soluble  up  to  a  high  temperature  they  cannot  be  removed  from 
the  feed  water  as  easily  before  entering  the  boiler  as  can  the 
carbonates.  The  sulphates  possess  very  active  cementing  quali- 
ties, and  not  only  form  a  very  hard  scale  themselves,  but  become 
mixed  with  mud  and  other  sediment,  cementing  it  also  into  a 
very  dense,  hard  scale.  Calcium  and  magnesium  sulphate  may 
be  removed  from  the  feed  water  in  a  closed  heater,  which  is  sup- 
plied with  steam  at  a  gage  pressure  of  about  55  or  60  Ib.  per 
sq.  in.  as  steam  at  this  pressure  has  a  temperature  9f  about 


290  STEAM  BOILERS 

300°  F.  They  may  also  be  removed  from  the  feed  water  by 
heating  in  an  open  feed-water  heater  before  entering  the  boiler 
and  then  adding  certain  chemicals  which  change  the  nature 
of  the  sulphates.  The  best  and  cheapest  chemical  for  this  pur- 
pose is  carbonate  of  soda  which  is  also  known  by  the  names  of 
soda  ash,  soda  crystals,  sal  soda,  washing  soda,  Scotch  soda, 
concentrated  crystal  soda,  crystal  carbonate  of  soda,  black  ash, 
and  alkali.  At  temperatures  above  200°  F.,  carbonate  of  soda 
or  soda  ash  acts  on  the  sulphate  of  calcium  and  magnesium,  and 
also  sodium  sulphate.  The  carbonates  thus  formed  become 
insoluble  and  deposit  at  this  temperature,  as  explained  above. 
The  sodium  sulphate  thus  formed  remains  in  solution  and  passes 
into  the  boiler  where  it  gradually  accumulates  in  the  water 
till  it  can  hold  no  more,  when  it  is  deposited.  Before  it  begins 
to  deposit,  however,  the  boiler  may  be  blown  down  and  refilled 
with  fresh  water.  The  Hartford  Steam  Boiler  Inspection  and 
Insurance  Company  states  that  with  an  average  water,  such  as 
that  of  Lake  Michigan,  requiring  1  Ib.  of  soda  ash  per  10-hour  day 
for  a  75-h.p.  horizontal  return  tubular  boiler,  the  boilers  should 
be  blown  down  two  gages  every  12  hours,  and  should  be  emptied 
and  refilled  with  water  not  less  than  once  in  3  weeks. 

214.  Chlorides. — Magnesium   chloride   gives   trouble  because 
of  its  cementing  properties.     The  other  chlorides  such  as  cal- 
cium, sodium,  and  potassium  give  little  trouble  from  incrusta- 
tion unless  allowed  to  concentrate  until  the  water  will  hold  no 
more  in  solution,  when  they  are  deposited  and  increase  the  bulk 
of  the  scale.     They  may,  however,  cause  foaming,  which  will 
be  greater  as  the  solution  becomes  more  concentrated.     Mag- 
nesium chloride  is  generally  supposed  to  have  a  corrosive  action 
on  the  steel  plates  of  the  boiler.     It  is  thought  that  it  reacts 
with  the  water,  under  the  influence  of  heat,  so  that  magnesium 
hydrate  and  hydrochloric  acid  are  formed,  the  acid  then  attack- 
ing the  metal  of  the  shell  and  tubes. 

215.  Effects  of  Impurities. — The  effects  of  various  impurities 
depend  on  the  nature  of  the  substances  precipitated  or  in  solu- 
tion.    They  will  all  fall  under  one  of  the  following  four  heads  : 

(1)  Precipitation  of  mud,  etc. 

(2)  Formation  of  scale. 

(3)  Formation  of  scum  which  causes  excessive  priming  or 
foaming. 

(4)  Corrosion  of  the  metal. 


BOILER  FEED  WATERS  291 

216.  Mud. — As  far  as  possible,  mud  should  be  removed  from 
feed  water  before  it  enters  the  boiler.     This  can  be  done  by  fil- 
tering the  water  or  passing  it  into  tanks  which  are  large  enough 
to  allow  the  water  to  remain  in  them  some  time,  when  the  mud 
will  collect  on  the  bottom.     Such  tanks  should  be  cleaned  from 
time  to  time.     If  allowed  to  enter  the  boiler,  provision  should 
be  made  to  catch  the  mud  and  blow  it  off  before  it  has  a  chance 
to  become  baked  on  the  heating  surface.     If  there  is  any  part 
of  the  boiler  where  the  circulation  is  sluggish  the  mud  will  settle 
there,  and  on  some  water-tube  boilers  a  mud-collecting  chamber 
is  provided.     Such  a  chamber  is  shown  in  Fig.  19  at  the  bottom 
of  the  back  header  of  the  Babcock  and  Wilcox  water-tube  boiler. 
If  the  mud  is  collected  and  blown  off,  the  only  evil  effect  from  it 
is  the  loss  of  heat  while  blowing  off  but,  if  the  mud  is  allowed  to 
bake  on  the  heating  surface,  it  lowers  the  heat  transmitting 
power  of  the  metal  very  much  and,  besides  a  loss  of  capacity 
and  efficiency,  it  may  cause  the  metal  to  be  blistered  or  burned. 

217.  Preventing  Scale. — The    formation    of    scale    and    the 
troubles  caused  by  it  have  already  been  explained.     The  feed 
water  should  be  analyzed  and  steps  taken  either  to  prevent  the 
scale-forming  elements  from  entering  the  boiler  or  to  cause  their 
deposit  within  the  boiler  in  a  form  that  will  not  adhere  to  the 
metal  but    can  readily  be  blown  out.     If    scale   has  already 
formed   within   a   boiler,   chemicals   should    be   introduced   to 
soften  the  scale  and  then  it  should  be  removed  by  washing,  if 
softened  sufficiently,  or  if  not,  by  mechanical  means.     If  the 
scale  is  very  hard  and  flinty  it  indicates  that   there  is  a  con- 
siderable percentage  of  the  sulphates  present.     The  carbonates 
form  a  very  soft  scale. 

The  amount  of  scale  that  will  be  deposited  in  a  boiler  by  even 
good  water  is  surprising.  Suppose  a  100-h.p.  boiler  is  using 
water  containing  only  8  grains  of  solid  matter  per  gallon.  The 
amount  of  water  used  per  month  will  be  about  (100X30X12X 
30)  -4-  8J  =  130,000  gal.  This  amount  will  deposit  about 
(130,000X8)^7000  =  149  Ib.  of  scale,  and  if  the  boilers  are 
operated  24  hours  a  day  there  will  be  about  300  Ib.  of  scale 
deposited  each  month. 

218.  Foaming  and  Priming. — A  boiler  is  said  to  foam  if  the 
steam  space  is  partially  filled  with  unbroken  bubbles  of  steam, 
and  to  prime  if  the  steam  carries  water  with  it  from  the  boiler. 

Foaming  is  caused  by  any  materials,  either  dissolved  in  the 


292  STEAM  BOILERS 

water  or  suspended  in  it,  which  retard  or  interfere  with  the 
free  escape  of  steam  from  the  water  in  the  boiler.  A  collection 
of  scum  on  the  surface  of  the  water  is  also  a  common  cause  of 
foaming.  Scum  may  be  caused  by  oil,  vegetable  matter,  or 
sewage  which  collects  on  the  surface  of  the  water,  forming  a 
coating  which  is  hard  for  the  steam  bubbles  to  break  when  they 
rise  to  the  surface.  If  the  water  contains  an  alkali,  and  any 
animal  or  vegetable  oil  becomes  mixed  with  it,  the  alkali  will 
change  the  oil  into  soap,  which  -forms  suds  and  causes  foaming. 
In  many  power  plants  the  exhaust  from  engines  or  pumps  is 
condensed,  collected  into  hot  wells,  and  fed  back  into  the  boilers. 
If  the  cylinders  are  lubricated  with  animal  or  vegetable  oil,  there 
is  danger  of  it  getting  into  the  boiler  and  causing  foaming.  For 
this  reason,  only  a  mineral  oil  should  be  used  in  the  cylinder 
but,  even  with  this,  great  care  should  be  taken  to  prevent  its 
entering  the  boiler,  as  it  is  a  frequent  cause  of  burned  plates. 
Oil  extractors  placed  in  the  exhaust  pipe  are  very  efficient  in 
removing  oil.  Open  feed-water  heaters  are  usually  provided 
with  oil  extractors,  and  feed  water  taken  from  such  heaters  is 
almost  entirely  free  from  oil. 

Foaming  may  also  be  caused  by  the  concentration  of  certain 
salts  in  the  water.  If  an  impure  water  is  fed  into  a  boiler,  the 
salts  will  be  left  behind  when  the  water  is  evaporated.  The  con- 
tinued evaporation  of  such  water  soon  causes  the  boiler  to  con- 
tain so  much  mineral  matter  that  it  can  no  longer  remain  dissolved 
in  the  water  but  is  precipitated  in  the  form  of  a  fine  powder,  and 
the  presence  of  these  small  particles  of  salts  may  cause  foaming  and 
priming.  Alkalies,  especially,  cause  foaming.  Sodium  sul- 
phate also  has  this  effect  and  this  salt  is  produced  as  a  by- 
product when  calcium  is  precipitated  with  soda  ash  or  sodium 
carbonate.  If  the  water  contains  considerable  quantities  of 
carbonate  of  lime  and  no  treatment  is  given  it  before  it  enters 
the  boiler,  this  lime  may  be  precipitated  in  the  boiler  itself, 
since  it  deposits  at  boiling  temperatures,  due  to  the  release  of 
carbonic  acid  gas  which  holds  it  in  solution.  When  released, 
this  carbonate  of  lime  is  in  a  very  finely  divided  state  and  may 
cause  foaming  a"nd  priming. 

Concentration  of  salts  in  a  boiler  may  be  prevented  by  fre- 
quently blowing  the  boiler  down  and  refilling  with  purer  water. 
There  is  sometimes  a  prejudice  against  blowing  boilers  down,  on 
account  of  the  heat  which  is  wasted  in  the  hot  water.  Consider- 


BOILER  FEED  WATERS  293 

ing  the  fact  that  economy  of  coal  is  more  dependent  upon  a 
good  heat  exchange  from  the  burning  coal  to  the  water  in  the 
boiler  than  upon  any  other  factor,  and  that  the  heat  exchange 
is  very  much  reduced  in  efficiency  by  any  sediment  in  the 
boiler,  it  will  be  seen  that  an  occasional  blowing  down  is  an 
economy,  as  well  as  preventing,  in  a  large  degree,  foaming  and 
priming. 

Foaming  has  been  found  to  occur  in  some  cases  where  a 
boiler  was  coated  with  scale  and  was  afterward  fed  with  a  very 
pure  water.  This  action  may  be  explained  by  the  fact  that  pure 
water  will  sometimes  dissolve  the  scale,  leaving  the  metal  of  the 
boiler  bare  in  places.  Such  bare  spots  transfer  heat  much  faster 
than  surrounding  parts  covered  with  scale,  hence  there  is  very 
violent  boiling  over  the  bare  spots  which  may  result  in  foaming 
or  priming. 

Chemical  treatment  of  feed  water  does  not  necessarily  create 
priming  conditions,  for  if  the  boilers  have  sufficient  capacity  and 
are  properly  handled  it  is  possible  to  feed  large  quantities  of 
chemicals  into  them  without  trouble.  At  the  same  time,  cer- 
tain types  of  vertical  boilers  are  especially  liable  to  prime  on 
account  of  their  small  disengagement  surface.  Priming  is,  in 
general,  caused  by  the  following  conditions,  all  of  which  should 
be  looked  after: 

Overloading, 

The  way  in  which  the  engine  is  operated, 

Presence  of  oil, 

Method  of  controlling  boiler  feed  pumps, 

Location  of  feed-water  inlet, 

Method  of  firing  under  forced  draft, 

Failure  to  blow  down  regularly  and  sufficiently, 

Failure  to  clean  the  boilers  regularly, 

Type  of  boiler, 

Water  level. 

219.  Corrosion. — Corrosion  is  most  often  caused  by  the  pres- 
ence of  a  free  acid  in  the  feed  water.  The  free  acid  may  re- 
sult from  the  supply  of  water  being  contaminated,  from  adulter- 
ants in  the  cylinder  oil  which  find  their  way  into  the  boiler,  or 
from  the  splitting  up  of  certain  salts  in  the  water. 

Water  coming  from  a  mine  or  passing  through  a  vein  of  ore 


294  STEAM  BOILERS 

containing  sulphur  may  become  charged  with  sulphuric  acid 
which  will  attack  the  metal  in  the  boiler.  Certain  acids  of  vege- 
table origin  may  find  their  way  into  the  feed  water  if  the  supply 
passes  through  a  marsh  or  bog  which  contains  decaying  vege- 
table matter.  Even  well  water  which  is  supposed  to  be  pure 
may  contain  acid  from  either  of  the  sources  mentioned  above. 
Some  grades  of  cylinder  oil  contain  adulterants  which  form 
fatty  acids  capable  of  attacking  metal.  Sea  water  contains 
magnesium  chloride  and  this  salt  is  readily  decomposed,  forming 
hydrochloric  acid.  A  similar  effect  is  also  produced  in  some 
waters  contaminated  with  sewage. 

All  water  contains  more  or  less  air,  which  is  liberated  when 
the  water  is  heated  and  which  attacks  metal  surfaces.  Air  ab- 
sorbed in  water  is  more  active  in  attacking  metal  than  free  air. 
This  is  probably  due  to  the  fact  that  more  oxygen  than  nitrogen 
is  absorbed  by  the  water  and  this  extra  quantity  of  oxygen 
attacks  the  metal  more  rapidly  than  a  like  quantity  of  free  air. 
As  air  is  driven  out  of  solution  at  a  lower  temperature  than 
that  required  to  form  steam  under  the  ordinary  pressures,  the 
corrosion  from  this  cause  will  be  greatest  in  those  parts  of  the 
boiler  where  the  circulation  is  sluggish. 

The  ordinary  ingredients  of  scale,  carbonate  and  sulphate  of 
lime,  have  little  or  no  direct  corrosive  action  unless  the  scale 
becomes  too  thick  and  causes  overheating.  In  fact  a  slight 
coating  of  these  salts  acts  as  a  protection  and,  in  some  cases 
when  the  water  fed  into  the  boiler  is  exceptionally  pure,  the  in- 
terior of  the  boiler  may  be  lime  washed  at  cleaning  time  with 
advantage. 

In  most  cases  the  corrosive  effect  of  water  containing  acids 
can  be  diminished  by  neutralizing  the  acid  with  an  alkali  such  as 
caustic  soda  or  soda  ash,  but  care  must  be  exercised  in  using 
alkali  because,  when  the  water  contains  any  alkali,  any  copper 
surfaces  with  which  it  comes  in  contact  will  be  rapidly  corroded 
if  the  circulation  is  poor,  since  the  alkali  will  dissolve  the  copper 
as  fast  as  it  oxidizes,  thus  keeping  a  fresh  surface  exposed  to 
the  action  of  the  oxygen. 

Another  frequent  cause  of  pitting  and  corrosion  is  a  galvanic 
action  which  goes  on  in  some  boilers.  This  may  be  stopped  by 
placing  pieces  of  zinc  in  various  parts  of  the  boiler.  The  zinc 
will  be  eaten  instead  of  the  steel  and,  therefore,  will  need  replac- 
ing frequently. 


BOILER  FEED  WATERS  295 

220.  Treatment  of  Feed  Waters. — In  case  the  feed  water  is 
known  to  contain  impurities,  a  sample  of  it  should  be  sub- 
mitted to  a  chemist  who  makes  a  specialty  of  analyzing  feed 
water,  for  analysis  and  prescription  for  the  remedy  to  be  applied. 
This  course  should  also  be  followed  in  the  case  of  a  new  plant. 
When  the  location  for  a  new  plant  is  to  be  chosen,  particular 
care  should  be  taken  to  secure  a  sufficient  supply  of  good 
water. 

The  term  "good"  as  applied  to  feed  water  is  only  relative,  but 
the  following  designations  are  generally  used,  based  on  the 
number  of  grains  of  incrusting  substance  in  each  gallon  of  the 
feed  water: 

Less  than  8  gr.  per  gallon Very  good. 

From  8  to  12  gr.  per  gallon Good. 

From  12  to  15  gr.  per  gallon Fair. 

From  15  to  20  gr.  per  gallon Poor. 

From  20  to  30  gr.  per  gallon Bad. 

More  than  30  gr.  per  gallon Very  bad. 

This  table  applies  to  calcium  carbonate,  magnesium  carbonate, 
and  the  chlorides.  For  water  containing  sulphate  of  calcium  or 
magnesium  in  large  percentages  of  the  total  impurities,  divide 
the  number  of  grains  by  4  for  the  same  rating. 

Water  containing  as  much  as  20  to  30  gr.  of  incrusting  materials 
to  the  gallon  should  never  be  used  unless  the  water  is  first 
purified. 

Very  often  the  trouble  with  impure  feed  waters  may  be  lessened 
considerably  by  intelligent  action  on  the  part  of  those  in  charge 
of  the  boilers. 

There  are  three  courses  of  procedure  open,  viz. : 

(1)  To  neutralize  the  acids  and  remove  the  solids  before  the 
water  is  allowed  to  enter  the  boiler. 

(2)  To  treat  the  water  with  chemicals  after  it  has  entered  the 
boiler,  with  a  view  of  lessening  or  preventing  the  formation  of 
scale. 

(3)  To  evaporate  the  water  and  remove,  at  regular  intervals, 
the  deposits  which  form  within  the  boiler. 

Unless  the  water  is  very  good  the  first  course  is  the  best. 

Free  acids  should  always  be  neutralized  before  the  water  enters 
the  boiler,  as  it  can  be  done  easier  outside  than  inside  the  boiler. 
This  may  best  be  done  by  adding  carbonate  of  soda  to  the  water, 


296  STEAM  BOILERS 

but  no  more  should  be  used  than  is  absolutely  necessary  because, 
as  noted  above,  it  will  cause  foaming  if  used  to  excess.  Water 
that  is  suspected  of  containing  acid  may  be  tested  by  dipping  a 
piece  of  blue  litmus  paper  in  it;  if  acid  is  present  the  paper  will 
turn  red.  If  there  are  scale-forming  impurities  present  with 
the  acid,  a  sample  of  the  water  should  be  submitted  to  a  chemist 
and  the  proper  treatment  determined. 

After  the  water  enters  the  boiler  it  may  be  treated  by  the 
addition  of  certain  substances  which  will  cause  the  impurities 
to  be  deposited  in  a  less  objectionable  form  than  if  left  untreated. 
When  prepared  by  a  competent  chemist  for  the  particular  water 
to  be  treated,  these  reagents  are  of  great  value,  but  the  indis- 
criminate use  of  boiler  compounds  or  "cure-alls"  is  not  to  be 
recommended. 

As  indicated  before,  carbonate  of  calcium  and  carbonate  of 
magnesium  may  be  precipitated  by  the  application  of  heat  to 
the  feed  water  before  it  enters  the  boiler.  They  may  also  be 
precipitated  by  the  addition  to  the  water  of  caustic  lime,  Ca(OH)  2, 
which  reduces  them  to  a  practically  insoluble  carbonate. 
Sodium  hydroxide,  or  caustic  soda,  NaOH,  accomplishes  the 
same  purpose. 

The  sulphates  of  calcium  and  magnesium  may  be  converted 
into  carbonates  by  the  addition  to  the  feed  water  of  soda-ash, 
Na2C03.  After  being  converted  into  carbonates  or  chlorides 
they  are  harmless  and  require  only  an  occasional  blowing  off 
in  order  to  prevent  too  great  an  accumulation. 

If  the  continued  use  of  impure  water  has  allowed  a  scale  to 
form,  some  form  of  solvent  must  be  used  to  loosen  it.  This 
should  be  done  by  feeding  in  a  small  portion  of  the  solvent  grad- 
ually rather  then  a  large  quantity  at  long  intervals.  ,  The  intro- 
duction of  30  Ib.  of  soda-ash  once  a  month  would  probably  cause 
violent  foaming  for  a  few  minutes,  but  if  only  1  Ib.  a  day  is 
used  no  harmful  effects  will  be  noticed.  The  proper  way  to 
introduce  the  solvent  is  to  attach  to  the  feed-pump  suction  an 
apparatus  to  feed  it,  just  as  cylinder  oil  is  fed  to  an  engine.  There 
are  a  number  of  such  devices  on  the  market  or  one  can  easily  be 
made. 

For  convenience  of  reference,  the  different  impurities  to  be 
found  in  feed  water  and  the  remedies  to  be  applied  are  collected 
in  the  following  table : 


BOILER  FEED  WATERS 


297 


Troublesome  substance 


Trouble 


Remedy 


Sediment,  mud,  clay,  etc Incrustation. 

Readily  soluble  salts i  Incrustation . 


Bicarbonates     of     lime,     mag- 
nesium and  iron. 
Sulphate  of  lime 


Chloride  and  sulphate  of  mag- 
nesium. 

Carbonate  of  soda  in  large 
quantities. 

Acid 

Dissolved    carbonic    acid    and 


Incrustation. . 


Incrustation.  . 


Incrustation  and  cor- 
rosion. 
Priming 

Corrosion 

Corrosion .  .  . 


oxygen. 
Grease  (from  condensed  water) .    Foaming 


Organic  matter  (sewage) 

Organic  matter 


Priming. . 
Corrosion . 


Filtration,  blowing  off. 

Blowing  off. 

Heating  feed.  Addition  of  caus- 
tic soda  or  lime. 

Addition  of  carbonate  of  soda,  or 
barium  chloride. 

Addition  of  carbonate  of  soda. 

Addition  of  barium  chloride. 

Alkali. 

Heating  feed  water.     Addition  of 

caustic  soda  or  slacked  lime. 
Slacked     lime     and     filtering. 

Carbonate  of  soda.     Substitute 

mineral  oil. 
Precipitate   with   alum,   or  ferric 

chloride,  and  filter. 
Precipitate   with   alum,   or  ferric 

chloride,  and  filter. 


221.  Boiler  Cleaning. — Even  though  some  method  of  feed- 
water  treatment  is  used,  a  boiler  will  need  cleaning  from  time 
to  time,  as  it  is  almost  impossible  to  prevent  some  of  the  scale- 
forming  material  from  entering  the  boiler.  Some  of  the  methods 
of  feed-water  treatment  noted  above  provide  for  feeding  certain 
chemicals  into  the  boiler  for  the  purpose  of  changing  the  nature 
of  the  deposit  from  a  hard  to  a  soft  scale.  Other  methods  remove 
the  subtsances  which  form  the  softer  scale  before  the  water  is 
fed  into  the  boiler,  leaving  the  materials  which  form  hard  scale 
to  be  deposited  inside  the  boiler.  While  these  methods  may 
reduce  somewhat  the  amount  of  scale,  they  cannot  entirely 
prevent  its  formation,  hence  the  necessity  for  cleaning  the 
boiler  occasionally.  At  the  same  time  that  scale  is  collecting 
on  one  side  of  a  tube,  soot  is  collecting  on  the  other  side,  and  it 
is  necessary  therefore  to  clean  both  the  inside  and  the  outside 
of  a  boiler,  since  both  soot  and  scale  interfere  with  the  passage 
of  heat  and  lower  the  efficiency  of  the  boiler. 

The  scale  deposited  in  boilers  varies  all  the  way  from  a  soft 
porous  scale,  that  can  be  removed  easily,  to  a  hard,  dense  scale 
which  is  difficult  to  cut  even  with  a  cold  chisel.  Fortunately, 
the  carbonates,  which  are  the  most  common  feed-water  im- 
purities, deposit  a  rather  soft  scale,  while  the  less  common 
sulphates  form  a  very  hard  scale  which  is  difficult  to  remove. 


298  STEAM  BOILERS 

While  the  removal  of  hard  scale  is  sometimes  a  very  tedious  job, 
it  should  never  be  slighted,  and  before  leaving  a  tube  the  one 
in  charge  of  the  cleaning  should  make  sure  it  is  thoroughly 
cleaned. 

The  method  of  cleaning  the  boiler  will  vary  somewhat,  depend- 
ing upon  the  kind  of  scale  to  be  dealt  with  and  also  the  type  of 
boiler.  In  general,  however,  the  boiler  can  be  cleaned  better  and 
in  less  time  by  the  use  of  mechanical  cleaners,  which  may  be  passed 
through  the  tube,  than  by  the  use  of  hand  operated  scrapers, 
which  were  used  to  a  considerable  extent  some  years  ago. 

There  are  two  distinct  kinds  of  mechanical  cleaners,  those 
which  hammer  upon  the  inside  of  the  tube  and  break  the  scale 
by  the  vibrations  in  the  tube,  and  those  which  remove  the  scale 
by  means  of  rotary  cutters,  the  former  being  best  adapted  to 
cleaning  fire-tube  boilers  and  the  latter  to  cleaning  water-tube 
boilers. 

Mechanical  cleaners  are  operated  by  means  of  water,  com- 
pressed air,  or  steam.  Those  operated  by  water  are  better  for 
cleaning  the  inside  of  tubes  in  a  water-tube  boiler,  as  the  waste 
water  from  the  cleaner  serves  to  wash  the  scale  out  of  the  tube  as  it 
is  removed.  Compressed  air  cleaners  are  suitable  for  removing 
soot  from  the  inside  of  the  tubes  of  fire-tube  boilers  where  the 
soot  has  become  so  hard  that  it  cannot  be  removed  by  scrap- 
ing. In  this  case  the  air  exhausted  from  the  cleaner  will  blow 
the  particles  of  soot  out  of  the  tube  as  fast  as  they  are  loosened, 
whereas  water  would  cause  them  to  gum  and  stick  to  the  tubes, 
where  they  would  be  baked  when  the  boiler  is  used  again.  Steam 
may  also  be  used  to  operate  cleaners  in  fire-tube  boilers  if  the 
boiler  is  hot,  but  it  should  not  be  used  if  the  tubes  are  cold,  as 
it  condenses  and  causes  the  soot  to  gum  and  stick  to  the  tubes. 

A  hammer  type  of  mechanical  tube  cleaner,  with  which  either 
air  or  steam  may  be  used,  is  shown  in  Fig.  165.  The  stem  or 
air  pipe  is  connected  to  the  coupling  A,  and  the  steam  or  air  ad- 
mitted to  the  valve  chamber  B,  where  the  valve  C  distributes 
it  through  the  ports  D  and  E  to  first  one  side  and  then  the  other 
of  the  piston  L,  giving  it  a  backward  and  forward  motion  across 
the  body  of  the  cleaner.  The  stem  G  of  the  hammer  passes 
through  the  piston  and  is  pivoted  at  H.  The  end  of  the  stem 
rests  in  a  recess  of  the  valve  and  serves  to  move  the  valve  across 
the  ports  D  and  E.  While  the  steam  or  air  is  being  admitted 
to  one  side  of  the  piston  it  is  being  exhausted  from  the  other 


BOILER  FEED  WATERS 


299 


side,  passing  through  the  port  to  the  inside  of  the  valve  and 
leaving  the  cleaner  through  the  opening  M.  In  operation,  the 
cleaner  is  inserted  in  the  end  of  the  tube  to  be  cleaned;  the 
steam  or  air  is  then  turned  on,  causing  the  piston  to  move  back 
and  forth,  carrying  with  it  the  hammer  J  which  strikes  the  tube 
a  hard  blow  first  on  one  side  and  then  on  the  other.  As  the 
hammer  strikes  from  3000  to  4000  blows  per  minute,  vibrations 
are  set  up  in  the  boiler  tube  which  loosen  the  scale,  and  break 
it  into  small  pieces.  The  speed  of  the  hammer  is  regulated  by 
admitting  a  greater  or  less  quantity  of  steam  or  air. 


Co  F 

FIG.  165. — Hammer  type  of  tube  cleaner. 

These  cleaners  are  made  in  several  sizes  to  suit  the  common 
sizes  of  boiler  tubes,  the  barrel  of  the  cleaner  being  slightly 
smaller  than  the  inside  of  the  tube.  Since  the  hammer  moves 
in  a  straight  line  across  the  tube,  it  is  necessary  to  keep  turning 
the  cleaner  in  order  to  remove  the  scale  from  all  parts  of  the  tube. 
As  the  cleaner  loosens  the  scale  by  vibrating  the  tube,  it  is  best 
to  have  the  inside  of  the  tube  clean  before  the  cleaner  is  inserted, 
in  order  that  the  hammer  may  strike  directly  on  the  metal  in- 
stead of  on  a  layer  of  soot  which  would  lessen  the  force  of  the 
blow.  As  an  objection  to  the  hammer  type  of  cleaner  it  is 
claimed  that  they  eventually  distort  the  tube  and  cause  it  to 
crystallize  and  weaken. 

A  common  form  of  rotary  tube  cleaner,  especially  adapted  for 
cutting  the  scale  from  the  inside  of  tubes  of  a  water-tube  boiler, 
is  shown  in  Fig.  166.  This  type  of  cleaner  is  known  as  a  hydrau- 
lic turbine  cleaner  because  it  is  run  by  a  small  water  turbine 
located  in  the  casing.  The  cleaner  is  made  in  different  sizes  to 
suit  the  different  sizes  of  boiler  tubes,  the  casing  being  a  little 
smaller  than  the  inside  of  the  tube.  In  operation,  water  is  led 
into  the  rear  end  of  the  casing  through  a  flexible  hose.  From 


300  STEAM  BOILERS 

the  chamber  located  in  the  end  of  the  casing  the  water  passes 
through  a  number  of  guide  channels  in  the  casing  A,  which 
direct  it  into  the  curved  passages  in  the  turbine  runner  B. 
This  causes  the  cutter  head,  which  is  fastened  to  the  runner,  to  re- 
volve at  a  high  speed.  After  passing  through  the  turbine,  the 
water  is  discharged  from  the  front  end  of  the  cleaner  and 
serves  to  wash  the  loosened  scale  from  the  tube.  The  cutter 
head  consists  of  a  main  body  which  revolves  about  the  central 
axis  F,  and  of  three  arms  M  which  carry  the  cutters  and  which 
are  pivoted  by  the  pins  0.  When  the  cutter  head  revolves,  the 
arms  M  are  thrown  outward  by  centrifugal  force,  causing  the 


FIG.  166.— Turbine  tube  cleaner. 

cutters  to  press  against  the  scale  and  cut  it  away.  Each  cutter 
arm  is  provided  with  two  cutters,  the  front  ones  being  tapered, 
and  the  rear  ones  straight.  Different  styles  of  cutters  for  vari- 
ous kinds  of  scale  are  supplied  with  each  cleaner. 

In  preparing  to  clean  boilers,  the  first  thing  to  do  is  to  cut  the 
boiler  out  of  service.  The  fires  should  then  be  drawn  and  the 
ash  pit  and  firing  doors  closed  tightly  to  prevent  the  entrance  of 
cold  air,  which  would  injure  the  boiler  by  cooling  it  too  quickly 
and  would  cause  the  surface  of  the  fire-brick  lining  to  spall,  or 
split  off.  The  stack  damper  may  be  left  open  to  carry  away  the 
small  amount  of  air  that  leaks  into  the  furnace.  The  boiler 
should  then  be  left  in  this  condition  to  cool  slowly,  requiring 
from  12  to  24  hours.  The  slower  the  boiler  is  allowed  to  cool 
the  less  danger  will  there  be  of  injuring  it.  If  for  any  reason  the 
boiler  must  be  cooled  more  quickly,  it  can  best  be  done  by  al- 
lowing the  water  to  leak  slowly  through  the  bottom  blow-off, 
at  the  same  time  pumping  in  cold  water  fast  enough  to  keep  the 
water  level  at  the  same  height.  This  will  cool  the  water  in  the 
boiler  gradually  and  uniformly  and  is  not  likely  to  injure  the 
boiler  from  unequal  contraction. 

As  soon  as  the  boiler  has  cooled  enough  to  permit  it,  the  ashes 
and  soot  should  be  blown  from  the  tubes.  To  keep  the  fire  side 
of  the  heating  surfaces  clean  is  of  equal  importance  with  keeping 


BOILER  FEED  WATERS  301 

the  water  side  clean.  Soot  is  a  poor  heat  conductor  and  if 
allowed  to  accumulate  on  tubes  will  greatly  reduce  their  power 
to  transmit  heat.  In  no  case  should  the  layer  of  soot  be  allowed 
to  exceed  1  / 16  in.  in  thickness.  In  the  case  of  a  water-tube  boiler, 
the  cleaning  can  best  be  done  by  means  of  a  steam  nozzle  inserted 
through  openings  in  the  side  walls. .  This  operation  should  not 
be  delayed  until  the  boiler  is  cold,  as  the  steam  will  then  be 
condensed  on  the  tubes,  and  wet  the  soot  and  ashes,  causing 
them  to  adhere  more  closely  than  ever.  In  the  case  of  a  fire- 
tube  boiler  the  soot  and  ashes  may  be  removed  from  the  tubes 
by  passing  a  scraper,  made  especially  for  this  purpose,  back 
and  forth  through  them.  To  prevent  chilling  the  tubes,  the 
fire  and  ash  pit  doors  should  be  kept  closed  while  the  soot  is 
being  removed.  After  the  boiler  is  cooled,  the  water  may  all  be 
drained  out  and  the  inside  washed  with  cold  water.  Before 
starting  to  remove  a  manhole  or  handhole  cover,  care  should 
always  be  taken  to  see  that  there  is  no  pressure  in  the  boiler 
and  that  there  is  no  vacuum  in  it.  This  may  be  done  by  opening 
the  top  gage  cock.  Many  serious  accidents  have  happened  from 
neglect  of  this  precaution. 

In  using  an  hydraulic  tube  cleaner,  the  largest  size  of  turbine 
that  will  pass  through  the  tube  should  be  used.  The  turbine  is 
inserted  in  the  tube,  the  operator  having  a  firm  grasp  on  the  hose 
connection  6  or  8  in.  from  the  end  of  the  tube  that  is  being 
cleaned.  The  water  is  then  turned  on  and  the  cutters  begin 
revolving  at  a  rapid  rate,  cutting  the  scale.  The  operator 
should  then  immediately  begin  to  move  the  cleaner  up  and  down 
or  forward  and  backward  in  the  tube  and  this  should  continue 
as  long  as  there  is  any  scale  in  the  tube.  As  the  scale  is  removed, 
the  water  from  the  turbine  washes  it  through  the  tubes,  where 
it  can  be  collected  and  removed.  The  cleaner  should  be  pushed 
forward  as  the  scale  is  removed,  but  this  should  not  be  done  too 
fast,  as  the  cleaner  will  jam  and  its  speed  and  cutting  power  be 
reduced.  The  operator  should  learn  to  judge  from  the  sound 
what  kind  of  surface  the  cleaner  is  working  on.  After  a  mechan- 
ical cleaner  has  been  used  it  should  be  washed  off  and  stored 
away  in  a  pail  of  oil  to  prevent  it  from  rusting. 

Certain  kinds  of  scale  will  bake  very  hard  on  the  tubes  and  their 
removal  is  extremely  difficult.  In  such  cases  it  is  often  best  to 
soften  the  scale  before  attempting  to  remove  it  with  a  cleaner. 
This  may  be  done  by  introducing  from  40  to  80  Ib.  of  carbonate  of 


302  STEAM  BOILERS 

soda  (ordinary  soda-ash),  depending  upon  the  size  of  the  boiler. 
The  safety  valves  should  then  be  blocked  open  so  no  pressure 
can  accumulate  and  the  water  should  be  heated  until  it  begins 
to  simmer.  In  bad  cases,  this  boiling  should  be  continued  for 
several  days.  The  scale  will  then  be  softened  so  that  it  may  be 
easily  cut.  The  boiler  must  be  thoroughly  washed  out  after 
using  the  soda-ash,  or  excessive  foaming  will  result. 

Kerosene  is  also  often  used  to  soften  scale.  The  best  way  to 
introduce  kerosene  is  to  fill  the  boiler  almost  full  of  water,  and 
then  pour  a  gallon  or  two  of  kerosene  on  top  of  it.  As  the  kero- 
sene is  lighter  than  the  water  it  will  stay  on  top.  By  opening 
the  blow-off,  the  water  in  the  boiler  will  gradually  sink  and  a 
film  of  oil  will  be  spread  over  all  the  inside  surfaces.  The  kero- 
sene will  attack  the  scale  and  loosen  it,  after  which  it  may  be 
readily  removed.  Kerosene  for  this  purpose  should  be  entirely 
free  of  acid  and  it  should  always  be  tested  by  inserting  blue  lit- 
mus paper.  If  the  paper  turns  red  there  is  acid  present  and  the 
kerosene  should  not  be  used.  Before  entering  a  boiler  after 
kerosene  has  been  used,  it  should  be  thoroughly  ventilated,  as 
very  explosive  gases  are  given  off  by  the  evaporation  of  the 
kerosene. 

If  cylinder  oil  should  get  into  a  boiler,  it  may  be  removed  by 
placing  soda-ash  in  it  and  raising  about  15  Ib.  steam  pressure. 
Occasionally  some  of  the  water  should  be  drawn  off  and  fresh 
water  added.  Under  no  circumstances  should  a  boiler  be  run 
if  there  is  oil  in  it,  as  oil  on  the  heating  surface  is  much  worse 
than  scale. 


CHAPTER  XVIII 
FEED- WATER  HEATERS 

222.  Feed -water  Heating. — The  office  of  a  boiler  is  to  evaporate 
water  and  the  heat  supplied  to  it  should  be  used  only  for  this 
purpose.     If,  in  addition  to  evaporating  the  water,  the  boiler  is 
also  called  upon  to  heat  the  feed  water  to  the  boiling-point  from 
some  lower  temperature,  the  capacity  of  the  boiler  will  be  reduced 
unless  it  contains  enough  additional  heating  surface  to  supply 
heat  to  the  feed  water.     In  other  words,  the  higher  the  tem- 
perature of  the  feed  water,  the  greater  will  be  the  capacity  of  a 
boiler  which  contains  a  given  amount  of  heating  surface.     If 
some  device  is  supplied  for  heating  the  feed  water  outside  the 
boiler,  it  is  equivalent  to  increasing  its  capacity,  but  the  gain  in 
capacity  is  secured  at  a  lower  cost,  because  a  feed-water  heater  of 
given    capacity   can   be   bought    cheaper  than   enough    boiler 
heating  surface  to  secure  the  same  result. 

With  hot  feed  water  there  will  also  be  less  wear  on  the  boiler 
from  strains  due  to  unequal  expansion  and  contraction  result- 
ing when  cold  feed  water  is  discharged  in  one  part  of  the  boiler 
while  other  parts  are  hot.  If  heat  which  would  otherwise  be 
wasted  is  used  for  heating  the  feed  water  before  it  enters  the 
boiler,  there  will  be  a  clear  gain  in  efficiency,  in  addition  to  the 
advantages  mentioned  above.  The  gain  in  heat,  from  heating 
the  feed  water  with  waste  heat,  will  amount  to  about  1  per 
cent  for  every  10°  F.  which  the  water  is  heated  and  this  gain 
in  heat  will  be  shown  by  a  reduction  of  an  equal  per  cent  in  the 
amount  of  coal  used.  While  the  purpose  of  a  feed-water  heater 
is  primarily  to  heat  the  feed  water,  in  many  cases  it  also  serves 
to  purify  it  by  causing  certain  impurities  to  be  deposited,  as 
noted  in  the  preceding  chapter. 

223.  Methods  of  Heating  Feed  Water. — The  methods  commonly 
employed  for  heating  feed  water  are    (1)  by  means  of  the  waste 
furnace  gases,  (2)  by  means  of  exhaust  steam,  (3)  by  means  of 
live  steam. 

224.  Economizers. — The  heat  in  the  waste  furnace  gases  may 
be  utilized  for  heating  feed  water  by  the  use  of  an  economizer, 

26  303 


304  STEAM  BOILERS 

which  has  been  previously  described.  The  heating  surface  in  an 
economizer  practically  forms  another  boiler,  working  within 
lower  limits  of  temperature,  and  is  thus  able  to  use  heat  which 
would  be  of  no  further  use  in  the  main  boiler.  The  saving 
effected  by  an  economizer  depends  upon  its  being  entirely 
separate  from  the  boiler  and  on  its  udng  heat  tnat  would  other- 
wise be  wasted.  An  economizer  heats  the  feed  water  entirely 
within  itself  by  means  of  h-^at  which  cannot  be  used  in  the 
boiler,  and  then  discharges  the  hot  water  into  the  boiler  to  be 
evaporated. 

Economizers  are  built  in  sizes  ranging  from  32  to  about  800 
tubes,  the  section  being  4,  6,  8,  10,  or  12  tubes  wide  and  varying 
in  depth  by  4  tubes.  Each  tube  contains  about  12.5  sq.  ft.  of 
heating  surface  and  has  a  volume  of  approximately  1  cu.  ft. 
and,  therefore,  will  hold  about  62  Ib.  of  water.  In  order  to  give 
satisfactory  efficiency,  the  economizer  for  a  boiler  plant  should 
have  sufficient  capacity  to  supply  one  hour's  feed.  Thus  a 
boiler  plant  which  uses  30,000  Ib.  of  water  per  hour  would 

soooo 

require    an    economizer    containing    about  — ^~  =4SO  tubes, 

approximately.  Another  approximate  rule  for  obtaining  the 
proper  size  of  economizer  for  a  given  boiler  plant  is  to  install 
6  sq.  ft.  of  economizer  heating  surface  for  each  boiler  horse- 
power. On  an  average,  the  feed  water  will  be  heated  by  an 
economizer  about  1/2°  for  each  degree  difference  in  tempera- 
ture of  the  flue  gases  entering  and  leaving  the  economizer. 
Thus,  if  the  flue  gases  leaving  the  boiler  and  entering  the  eco- 
nomizer have  a  temperature  of  500°  F.  and  the  waste  gases 
leaving  the  economizer  have  a  temperature  of  200°  F.,  the  feed 
water  will  be  increased  in  temperature  about  one-half  of  the 
difference,  or  (500-200)  -^2  =  150°.  The  feed  water  should  not 
be  supplied  to  an  economizer  at  a  lower  temperature  than  about 
90°  F.,  as  the  tubes  will  be  chilled  to  such  an  extent  that  moisture 
will  condense  on  them  and  make  it  difficult  to  remove  the  soot. 
If  the  supply  of  water  can  be  obtained  only  at  a  lower  temperature 
than  90°,  some  means  should  be  provided  for  heating  it  before 
it  enters  the  economizer. 

225.  Exhaust  Steam  Heaters. — The  exhaust  from  engines  and 
feed  pumps  is  extensively  used  for  heating  feed  water.  The  feed 
water  may  be  heated  entirely  by  exhaust  steam,  or  the  exhaust 
steam  heater  may  be  used  in  connection  with  an  economizer, 


FEED-WATER  HEATERS  305 

in  which  case  the  feed  water  is  heated  as  much  as  possible  in  the 
exhaust  heater  and  is  then  passed  through  an  economizer,  in 
which  its  temperature  is  raised  further. 

It  has  been  shown  in  the  preceding  chapter  that  heating  the 
feed  water  serves  to  purify  it  of  certain  impurities,  but  the 
principal  function  of  an  exhaust  feed-water  heater  is  to  utilize 
heat  whi^h  would  otherwise  be  wasted.  This  saving  will  amount 
to  about  1  per  cent  for  every  10°  that  the  feed  water  is  heated. 
More  exactly,  the  per  cent  of  saving  from  heating  the  feed 
water  by  exhausted  steam  may  be  calculated  by  the  formula 


in  which 

G  =  the  per  cent  of  gain  or  saving 

H  =  ihe  total  number  of  heat  units  above  32°  in  1  Ib.  of  exhaust 

steam 

£0=the  temperature  of  the  feed  water  before  being  heated 
^==the  temperature  of  the  feed  water  after  being  heated  by 

the  exhaust  steam. 

Example  :  What  would  be  the  per  cent  of  saving  from  heating 
feed  water  which  has  a  temperature  of  40°  F.  by  means  of 
exhaust  steam  having  a  pressure  of  16  Ib.  per  sq.  in.  absolute, 
the  final  temperature  of  the  feed  water  being  205°  F.? 

Solution:  The  total  heat  of  1  Ib.  of  steam  at  16  Ib.  pressure  is 
1148  B.t.u. 


=  10°         &    100X  nsr  14-47 


It  must  be  understood  that  this  formula  gives  only  the  saving 
of  heat  and  does  not  take  into  account  the  first  cost  of  the  heater 
nor  its  cost  of  operation.  These,  however,  are  small  compared 
with  the  benefits  derived,  so  there  will  usually  be  a  considerable 
net  saving.  Besides  the  direct  saving  of  heat  noted  above, 
an  additional  advantage  is  gained  by  feeding  hot  water  to  a 
boiler,  in  that  the  strains  from  unequal  expansion  and  contraction 
will  not  be  so  great. 

Exhaust  steam  feed-water  heaters  may  be  classified  according 
to  construction  as:  (1)  open  heaters,  in  which  the  water  and  steam 
mingle  in  the  same  chamber  and  the  steam  gives  up  its  heat  by 
condensation;  (2)  closed  heaters,  in  which  the  water  and  steam 


306  STEAM  BOILERS 

are  in  separate  chambers  or  pipes  and  the  steam  gives  up  its 
heat  by  conduction.  Open  heaters  may  also  be  classified  accord- 
ing to  the  method  of  connecting  them  to  the  exhaust  piping  as: 
(1)  induced  heaters,  in  which  only  enough  steam  to  heat  the 
feed  water  passes  into  the  heater,  the  remainder  going  through 
a  by-pass ;  (2)  through  heaters,  in  which  all  of  the  exhaust  passes 
into  the  heater,  that  which  is  not  condensed  in  heating  the 
feed  being  allowed  to  pass  out  of  the  heater  again.  Closed 
heaters  are  nearly  always  connected  as  through  heaters. 

226.  Open  Heaters. — A  common  form  of  exhaust  steam  open 
heater  is  illustrated  in  Fig.  167.  This  heater,  which  is  known 
as  the  Cochrane  heater,  consists  of  a  cast-iron  case  into  the  top 
of  which  is  fitted  a  series  of  trays  over  which  the  feed  water 
trickles,  and  at  the  bottom  of  which  there  is  storage  space  for 
the  hot  feed  water,  and  filtering  material  for  catching  any 
impurities  which  may  be  thrown  out  of  the  water  by  heating  it. 
The  steam  enters  through  the  exhaust  inlet  at  the  side,  where  it 
strikes  a  baffle  which  catches  most  of  the  oil  carried  by  the 
exhaust  steam  and  drains  it  into  the  oil  reservoir  located  at  the 
side  and  near  the  bottom.  The  oil  reservoir  is  provided  with  a 
float  valve  which  automatically  empties  it  when  the  oil  and 
water  reach  a  certain  height.  The  exhaust  steam  then  passes 
around  the  baffle  and  enters  the  heater  just  below  the  series  of 
pans,  where  it  rises  to  the  outlet,  mingling  with  and  heating  the 
feed  water  trickling  from  the  pans.  As  the  water  is  heated, 
certain  impurities  are  deposited,  part  collecting  on  the  pans  and 
part  falling  to  the  bottom  of  the  heater,  wheie  they  are  filtered 
from  the  water  before  it  enters  the  boiler.  The  pans  may  be 
removed  for  cleaning. 

The  water  in  the  storage  space  is  maintained  at  a  constant 
level  by  means  of  a  float  valve  attached  to  the  cold  water  supply 
and  by  means  of  an  overflow  which  empties  into  the  oil  reservoir. 
Any  oil  that  may  pass  the  oil  separator  will  collect  on  top  of  the 
water  in  the  storage  space  and  will  be  skimmed  off  through  the 
overflow  and  be  discharged  into  the  oil  reservoir.  Fresh  water 
enters  through  a  pipe  near  the  top  and  is  discharged  into  the  pans. 
If  the  heater  is  connected  to  a  heating  system,  as  is  often  done, 
the  condensation  from  the  radiators  is  returned  directly  to  the 
pans  and  only  enough  fresh  water  is  added  to  keep  the  water  in 
the  storage  space  at  a  constant  level. 

Fig.  168  shows  an  open  heater  of  the  type  just  described,  con- 


FEED-WATER  HEATERS 


307 


nected  as  a  through  heater  and  supplying  a  heating  system  with 
exhaust  steam.  The  exhaust  from  the  main  engine  enters  the 
heater  directly,  while  the  exhaust  from  the  feed  pump  is  connected 


FIG.  167. — Open  feed-water  heater  and  purifier. 

into  the  exhaust  from  the  main  engine  and  is  thus  also  util- 
ized in  heating.  Whatever  steam  is  needed  for  heating  the  feed 
water  is  condensed  in  the  heater,  falls  into  the  storage  space 


308 


STEAM  BOILERS 


with  the  feed  water,  and  is  thus  returned  to  the  boiler.  The 
remainder  of  the  exhaust  steam  passes  into  the  heating  system 
through  the  main  exhaust  pipe,  which  also  extends  oustide  the 


TO  ATMOSPMCHC 


FIG.  168. — Open  feed-water  heater  connected  to  heating  system. 

building.  As  steam  is  condensed  in  the  radiators,  a  partial 
vacuum  is  formed  in  them  and  more  steam  flows  in  from  the  ex- 
haust pipe.  The  condensation  from  the  radiators  is  drained 


FEED-WATER  HEATERS 


309 


back  to  the  heater,  where  it  is  heated  by  the  exhaust  steam  and  is 
again  fed  into  the  boiler.  If  there  is  more  exhaust  steam  than 
is  needed  to  heat  the  feed  water  and  the  building,  the  remainder 
passes  to  the  atmosphere  through  a  back  pressure  valve  which 
is  held  closed  by  a  weight  and  by  the  pressure  of  the  atmosphere 
as  long  as  the  pressure  in  the  heating  system  is  less  than  a 
fixed  amount,  but  which  opens  automatically  as  soon  as  the 
pressure  rises  above  that  amount.  In  case  there  would  not 
be  enough  exhaust  steam  to  heat  the  building  at  all  times,  a 


FIG.  169. — Open  induced  heater. 

supplementary  live  steam  connection  is  made  between  the 
boiler  and  the  exhaust  pipe  after  it  leaves  the  heater,  in  order  to 
supply  more  steam  to  the  heating  system  when  needed.  The 
heating  system  does  not  necessarily  form  a  part  of  the  exhaust 
system  as  shown.  If  no  heating  system  is  connected,  the 
exhaust  pipe  from  the  heater  passes  directly  to  the  atmosphere. 
Fig.  169  illustrates  the  method  of  connecting  an  open  induced 
heater,  in  which  only  enough  steam  to  heat  the  feed  water  enters 
the  heater,  the  remainder  passing  directly  to  the  heating  system 
or  to  the  atmosphere.  In  connecting  a  heater  in  this  manner, 
it  is  necessary  to  provide  a  vent  pipe  at  the  top  of  the  heater  to 
prevent  it  from  becoming  air-bound.  The  principal  advantage 


310  STEAM  BOILERS 

in  connecting  a  heater  in  this  manner  is  that  the  heater  may  be 
cut  out  of  service  for  cleaning  or  repairs  without  shutting  down 
the  plant. 

Fig.  170  shows  the  Pittsburg  heater,  which  is  the  same  in 
principle  as  those  already  shown  but  which  differs  somewhat 
in  construction.  This  heater  has  circular  pans  and  shell,  the 
feed  water  is  sprayed  on  the  pans  from  above,  trickles  over  their 
edges  and  falls  in  finely  divided  particles  to  the  storage  space 
below.  The  exhaust  steam  rises  through  the  falling  water, 


FIG.  170. — Pittsburgh  feed-water  heater. 

which  it  heats.  The  pans  are  cleaned  through  a  door  in  the 
side  of  the  heater,  and  it  is  not  necessary  to  remove  them  for 
this  purpose  as  they  are  pivoted  to  a  central  stem,  about  which 
they  may  be  revolved,  thus  making  all  parts  of  them  readily 
accessible.  These  heaters  are  provided  with  an  oil  separator 
on  the  outside  of  the  shell,  and  with  a  skimmer  inside  for  remov- 
ing oil  from  the  surface  of  the  water.  These  heaters  may  be 
connected  either  as  through  or  as  induced  heaters. 

Another  common  form  of  open  feed  water  heater  which  may 


FEED-WATER  HEATERS  311 

be  connected  either  as  a  through  or  an  induced  heater  is  shown 
in  Fig.  171.  This  Hoppes  heater,  as  it  is  called,  consists  of  a 
cylindrical  shell  placed  horizontally,  and  fitted  with  a  series  of 
trough-shaped  pans  placed  one  above  another.  In  the  larger 
size  of  heaters  these  pans  are  made  in  sections  for  ease  of  hand- 
ling. The  feed  water  enters  the  top  pan,  filling  it  and  over- 
flowing the  edges  and  through  openings  in  the  center,  while  the 
steam  circulates  among  the  pans,  heating  the  feed  water  as  it 
drops  from  one  pan  to  another.  As  the  water  overflows  from 
the  pans  it  flows  in  a  thin  sheet  along  the  bottom  of  the  pans 


FIG.  171. — Hoppes  feed-water  heater. 

until  the  lowest  point  is  reached,  when  it  drops  to  the  pan  be- 
neath. The  scale-forming  material  that  is  removed  by  the  heat 
collects  both  inside  the  pans  and  on  the  bottoms.  The  head  of 
the  heater  is  bolted  on  and  may  be  removed,  thus  allowing  access 
to  the  pans,  which  may  be  readily  removed  for  cleaning.  When 
used  with  exhaust  steam  these  heaters  are  fitted  with  a  baffle 
plate  oil  separator  placed  inside  the  shell  and  in  front  of  the 
exhaust  steam  inlet.  A  skimming  device  is  also  supplied  with 
these  heaters  for  removing  any  oil  that  may  collect  on  the  sur- 
face of  the  water  inside  the  heater. 


312  STEAM  BOILERS 

227.  Temperature  of  Feed  Water.  —  If  there  is  sufficient  steam, 
the  feed  water  in  an  open  heater  maybe  heated  to  a  temperature 
within  3°  or  4°  of  that  of  the  steam.  Thus  with  steam  supplied 
at  atmospheric  pressure,  the  temperature  of  the  water  leaving 
an  open-feed  water  heater  may  be  as  high  as  209°  F.  The 
amount  of  steam  condensed  in  heating  the  feed  water  will  depend 
both  upon  the  pressure  of  the  steam  in  the  heater  and  upon  the 
temperature  of  the  entering  feed  water. 
This  amount  may  be  calculated  by  the  following  formula 

WX(t-t0) 


~ 


.9X(H- 


In  which   S  =  weight  of  steam  condensed  in  heating  the  feed  water 
W  =  weight  of  feed  water  to  be  heated 
t  =  temperature  of  feed  water  leaving  heater 
t'0=  temperature  of  feed  water  entering  heater 
H  =  total  heat  of  1  Ib.  of  steam  at  the  pressure  existing 
inside  the  heater. 

This  formula  allows  for  a  loss  by  radiation  and  leakage  of  10 
per  cent  of  the  heat. 

Example  :  A  power  plant  consists  of  500  h.p.  of  engines 
using  24  Ib.  of  steam  per  horse-power  per  hour,  and  pumps 
which  use  15  per  cent  as  much  steam  as  the  engines.  The  ex- 
haust from  both  engines  and  pumps,  having  a  pressure  of  16 
Ib.  absolute,  is  turned  into  the  heater.  How  much  exhaust 
steam  will  be  condensed  in  heating  the  feed  water  if  the  water 
entering  the  heater  has  a  temperature  of  110°  F.  and  is  heated 
to  212°  F.? 

Solution:  W  =  500X24X1.  15  -13800  Ib.  of  feed  water  to  be 

heated  per  hour 
#  =  1147.9  from  steam  tables 
£  =  212° 
t0  =  UO° 

13800X(212-110) 

=  .9X  (1147.9-212  +  32)  = 

i  (\~\  f\ 
As  this  only  is  =11.7  per  cent  of  the  exhaust  steam,  the 

looOU 

remaining  88.3  per  cent  or  12,185  Ib.  per  hour  could  be  used  in  a 
heating  system,  or  wasted  into  the  atmosphere. 

228.  Closed  Heaters.  —  Closed  heaters  may  be  classified  as  (1) 


FEED-WATER  HEATERS 


313 


steam-tube,  in  which  the  steam  flows  through  the  tubes  while 
the  water  circulates  on  the  outside,  and  (2)  water-tube,  in  which 
the  water  flows  inside  the  tubes  while  the  steam  is  on  the  outside. 
229.  Steam  Tube  Heaters. — The  steam-tube  class  of  heaters  is 
illustrated  by  the  Otis  feed  water  heater  shown  in  Fig.  172 
This  heater  consists  of  a  vertical  cylindrical  shell  fitted  with  two 
sets  of  seamless  drawn  brass  steam  tubes.  The  exhaust  steam 


FIG.  172. — Otis  feed-water  heater. 

enters  at  the  top  and  passes  down  the  first  set  of  tubes  to 
the  chamber  at  the  bottom.  It  then  rises  through  the  other 
set  of  tubes  to  the  outlet,  thus  passing  the  length  of  the  heater 
twice.  The  chamber  at  the  bottom  is  for  the  purpose  of  catch- 
ing the  oil  and  water,  which  may  be  drained  from  the  heater  by 
means  of  the  waste  pipe.  The  tubes  are  curved  to  take  up  the 
expansion.  The  feed  water  enters  near  the  bottom  of  the  shell, 
circulates  around  the  steam  tubes,  and  leaves  near  the  top. 


314 


STEAM  BOILERS 


Another  type  of  steam-tube  feed  water  heater  is  shown  in  Fig. 
173,  which  represents  a  Baragwanath  steam  jacketed  heater. 
This  heater  consists  of  two  vertical  cylindrical  drums,  placed  one 
within  the  other,  the  inner  one  being  fitted  with  a  series  of  straight 
tubes  which  pass  from  one  end  of  it  to  the  other.  Exhaust 


FIG.  173. — Baragwanath  steam  jacketed  heater. 


steam  enters  at  the  bottom  through  A,  passes  up  through  the  set 
of  tubes  to  the  top,  and  then  to  the  bottom  again  through  the 
annular  space  between  the  two  drums.  The  feed  water  enters 
the  inner  drum  through  C,  filling  the  space  around  the  steam  tube, 
and  leaves  near  the  top  at  D.  E  is  a  scum  blow-off  for  the  inner 
drum,  G  is  the  bottom  drain  for  the  inner  drum,  and  H  a  drain 
for  the  jacket  or  space  between  the  two  drums.  Since  steam 


FEED-WATER  HEATERS  315 

circulates  through  the  tubes  and  around  the  inner  drum,  they 
will  be  at  approximately  the  same  temperature  and  there  will  be 
very  little  unequal  expansion  between  them;  hence  there  is  no 
necessity  for  allowing  for  expansion  in  the  tubes. 

Steam-tube  heaters  that  are  to  be  used  with  exhaust  steam 
should  have  an  oil  separator  connected  in  the  exhaust  pipe  be- 
tween the  engine  and  heater,  in  order  to  remove  the  oil  before  it 
reaches  the  tubes.  Oil  collecting  on  the  inner  surface  of  the 
tubes  greatly  reduces  their  power  to  conduct  heat,  and  hence 
lowers  the  efficiency  of  the  heater.  A  serious  objection  to  the 
use  of  steam-tube  heaters  with  water  containing  lime,  is  the  diffi- 
culty of  removing  the  deposit  of  lime  which  collects  on  the  out- 
side of  the  tubes  and  which  has  the  effect  of  reducing  their  power 
to  conduct  heat. 

230.  Water-tube  Heaters. — Water-tube  heaters  are  made  in  a 
variety  of  forms,  having  straight  tubes  or  coils.  Fig.  174  repre- 
sents the  Goubert  straight  tube  heater.  It  consists  of  a  vertical 
cylindrical  shell  fitted  with  a  series  of  brass  tubes.  The  tubes 
are  held  in  steel  headers  and,  being  shorter  than  the  shell,  a  com- 
partment is  left  at  each  end  of  the  heater.  These  compartments 
are  divided  by  a  number  of  partitions  which  divide  the  tubes  into 
sets  and  thus  cause  the  water  to  circulate  through  them  several 
times.  The  feed  water  enters  at  the  bottom,  flowing  upward 
through  the  first  set  of  tubes,  downward  through  the  second,  and 
so  on  till  the  outlet  at  the  top  is  reached.  Exhaust  steam  enters 
the  shell  near  the  bottom,  fills  the  entire  space  around  the  tubes, 
and  leaves  near  the  top.  A  drain  is  provided  for  each  compart- 
ment and  also  for  the  steam  space.  Since  the  shell  is  in  contact 
with  steam  while  the  tubes  are  in  contact  with  both  steam  and 
water,  the  shell  will  expand  more  than  the  tubes.  This  unequal 
expansion  is  taken  up  by  a  flexible  connection  between  the  top 
tube  plate  and  the  shell,  the  bottom  tube  plate  being  fastened 
rigidly  to  the  shell,  thus  forcing  all  the  movement  to  take  place 
at  the  top  connection. 

Fig.  175  illustrates  the  National  water-tube  heater,  in  which  the 
tubes  are  bent  into  coils.  The  coils  are  made  of  copper  pipe  and 
their  ends  are  brazed  to  gun  metal  manifolds.  Exhaust  steam 
enters  the  heater  at  the  bottom  of  the  casing,  surrounds  the  tubes, 
and  leaves  at  the  top. 

The  efficiency  of  water-tube  heaters  is  also  greatly  reduced  if 
oil  is  allowed  to  collect  on  the  tubes,  and  for  this  reason  it  is 


316 


STEAM  BOILERS 


BLOW 


FIG.  174. — Goubert  feed- water  heater. 


FEED-WATER  HEATERS  317 

necessary  to  place  an  oil  separator  in  the  exhaust  pipe  leading  to 
them,  if  "exhaust  steam  is  used  to  heat  the  water.  The  greatest 
objection  to  these  heaters  is  the  difficulty  of  removing  scale  from 
them,  if  used  with  impure  feed  water. 

Any  of  the  closed  heaters  described  here  may  be  connected 
into  the  exhaust  of  either  a  condensing  or  noncondensing  engine, 
but  if  the  engine  exhausts  into  a  partial  vacuum,  care  must  be 
taken  that  the  heater  is  air-tight  between  the  steam  and  water 
sides,  as  there  is  danger  of  the  vacuum  being  destroyed  by  the 
leakage  of  air. 


FIG.  175. — National  feed-water  heater. 

231.  Live  Steam  Heaters. — There  is  no  gain  in  economy  from 
heating  the  feed  water  with  live  steam,  because  the  heat  is  taken 
from  the  boiler,  put  in  the  feed  water,  and  returned  directly  to  the 
boiler.  In  fact,  there  will  actually  be  a  loss  of  heat  by  radiation 
in  such  a  process.  For  this  reason,  live  steam  feed-water  heaters 
are  installed  only  when  the  water  can  be  purified  by  heating  it  to 
a  high  temperature.  Besides  purifying  the  feed  water,  certain 
indirect  advantages  are  derived  from  heating  the  feed  water  with 
live  steam,  consisting  in  preventing  stresses  due  to  cold  feed  water 
being  fed1  to  the  boiler,  and  increased  capacity  by  feeding  hot 
water. 


318  STEAM  BOILERS 

Any  of  the  closed  feed-water  heaters  previously  described 
could  be  used  with  live  steam  if  built  strong  enough  to  withstand 
the  pressure,  and  if  provided  with  a  safety  valve  and  an  air  vent, 
but  with  the  water-tube  type  there  would  be  a  serious  difficulty 
in  removing  the  scale.  The  open  heater  shown  in  Fig.  171  is 
often  constructed  and  used  as  a  live  steam  heater  and  purifier. 
When  so  constructed,  it  is  provided  with  a  safety  valve  to  relieve 
the  pressure  if  it  should  become  too  high  and  the  shell  and  heads 
are  made  of  steel  plates.  An  air  vent  is  also  necessarj*,  as  the 
feed  water  will  contain  some  air  which  will  be  released  in  the 
heater  and  would  cause  it  to  become  air-bound  unless  relieved. 
When  used  with  live  steam,  the  action  of  this  heater  is  the  same 
as  with  exhaust  steam,  except  that  the  water  is  heated  to  a  higher 
temperature.  No  provision  need  be  made  for  oil  separation,  as 
the  steam  is  taken  directly  from  the  boiler. 

An  open  live  steam  heater  should  be  installed  so  its  lowest  part 
is  2  or  3  ft.  above  the  water  line  in  the  boiler,  in  order  that  the 
water  may  run  into  the  boiler  by  the  force  of  gravity.  The  feed 
pipe  leading  to  the  boiler  should  be  taken  from  the  bottom  of  the 
heater  and  should  run  straight  down  below  the  water  line  of  the 
boiler  before  any  branches  are  taken  off.  It  should  be  provided 
with  a  check  valve  to  prevent  water  from  flowing  in  the  wrong 
direction,  and  also  stop  valves  and  a  by-pass  so  the  heater  may  be 
cut  out  of  the  feed  system  for  cleaning,  and  water  pumped  di- 
rectly into  the  boiler. 

An  economical  arrangement  is  to  provide  two  of  these  heaters, 
one  connected  to  the  exhaust  from  the  pump  and  heating  the 
feed  water  with  exhaust  steam,  the  pump  taking  its  supply  of 
water  from  this  heater  and  pumping  it  into  the  second  heater, 
which  is  supplied  with  live  steam  from  the  boiler.  By  doing  this, 
the  live  steam  heater  will  remove  only  the  harder  scale-forming 
materials  from  the  water  and  it  will  not  require  cleaning  so  often. 
In  addition  to  this,  the  heat  in  the  exhaust  from  the  pump  will  be 
utilized  and  a  supply  of  hot  water  will  be  available  when  the  live 
steam  heater  is  cut  out  for  cleaning. 


CHAPTER  XIX 


INSPECTION  AND  CARE  OF  BOILERS 

232.  Defects  in  Boilers. — A  study  of  defects  in  boilers  as 
revealed  by  inspection  and  examination  after  explosion  is  both 
interesting  and  instructive.  It  shows  what  defects  are  most 
likely  to  occur  and,  therefore,  informs  the  fireman  what  details 
need  particular  attention  in  his  care  of  the  boiler;  it  also  informs 
the  inspector  where  defects  will  most  likely  be  found  and,  there- 
fore, what  things  should  receive  closest  attention.  The  following 
table,  showing  a  summary  of  results  of  boiler  inspections  made 
by  the  Hartford  Steam  Boiler  Inspection  and  Insurance  Com- 
pany during  the  year  1907,  is  instructive,  as  it  shows  the  number 
of  boilers  in  which  various  defects  were  found  and  also  the  num- 
ber and  per  cent  that  were  in  a  dangerous  condition. 

SUMMARY  OF  REPORT  OF  INSPECTIONS  FOR  1907,  HARTFORD  STEAM  BOILER 
INSPECTION  AND  INSURANCE  CO; 


Number 
found 
defec- 
tive 

Per  cent 
of  total 
number 

In  dan- 
gerous 
condi- 
tion 

Percentage 
of  dan- 
gerous to 
defective 

Cases  of  deposit  of  sediment 

18  917 

11  88 

1  315 

6  95 

Cases  of  incrustation  and  scale 

38427 

24  01 

1  333 

3  47 

Cases  of  internal  grooving 

3  010 

1  89 

258 

8  57 

Cases  of  internal  corrosion 

12  802 

8  04 

528 

4  13 

Cases  of  external  corrosion  
Defective  braces  and  stays  
Defective  settings  
Furnaces  out  of  shape  
Fractured  plates  
Burned  plates  
Laminated  plates  

10,230 
2,219 
6,363 
7,564 
3,551 
4,878 
898 

7.04 
1.39 
3.99 
4.74 
2.23 
3.06 
.56 

768 
578 
699 
396 
568 
499 
92 

7.53 
26.10 
11.00 
5.17 
16.00 
10.22 
10  23 

Cases  of  defective  riveting  

3,582 

2.25 

823 

23  00 

Defective  heads  

1,764 

1.11 

238 

13  49 

Leakage  around  tubes"  

11,357 

7.14 

1,599 

14  09 

Cases  of  defective  tubes  

8,266 

5.18 

3,054 

37.00 

Tubes  too  light 

1  947 

1   22 

563 

28  93 

Leakage  at  joints 

5  557 

3  49 

430 

7  74 

Water  gages  defective  
Blow-offs  defective  
Cases  of  deficiency  of  water  
Safety  valves  overloaded  
Safety  valves  defective  
Pressure  gages  defective  

3,008 
4,216 
413 
1,231 
1,211 
7,651 

1.89 
2.67 
.25 

.77 
.76 
4.8 

707 
1,250 
156 
415 
407 
465 

23.46 
29-.  63 
37.78 
33.70 
33.60 
6.08 

Without  pressure  gao'es 

194 

12 

194 

100  00 

Unclassified  defects 

27 

02 

10 

37  04 

Total       

159,283 

17,345 

27 


319 


320  STEAM  BOILERS 

The  defects  noted  in  this  table  may  be  roughly  divided  into 
three  classes  as:  (1)  those  due  to  the  feed  water,  (2)  those  due  to 
the  mechanical  features  and  management,  and  (3)  those  due  to 
defective  boiler  fittings.  Of  the  defects  shown  in  this  table, 
about  53  per  cent  were  due  to  the  feed  water  and  external  cor- 
rosion, while  the  mechanical  features  and  management  were  the 
cause  of  about  41  per  cent  and  the  defective  fittings  caused  only 
about  6  per  cent.  Of  those  found  defective  from  the  feed  water 
only  a  comparatively  small  percentage  were  in  a  dangerous 
condition,  showing  that  the  troubles  arising  from  impure  feed 
water  are  well  known  and  that  precautions  are  generally  taken  to 
clean  the  boilers  when  impure  water  is  used.  Of  those  boilers 
which  were  defective  from  mechanical  causes,  a  large  percentage 
were  in  a  dangerous  condition,  which  shows  that  such  defects 
are  more  likely  to  be  overlooked  by  the  firemen,  perhaps  because 
they  are  more  apt  to  be  hidden  and  not  give  warning  of  their 
existence.  A  very  large  percentage  of  the  boilers  found  de- 
fective due  to  the  condition  of  the  fittings,  were  in  a  dangerous 
condition,  which  points  to  the  fact  that  these  small  parts  of  a 
boiler  plant  should  receive  very  careful  attention  from  the 
fireman. 

Most  of  the  defects  resulting  from  the  use  of  impure  feed 
water  have  been  considered  in  another  chapter  and  the  means  of 
preventing  them  indicated.  However,  grooving  occurs  under 
such  a  variety  of  conditions  that  a  consideration  of  it  has  been 
left  until  this  time. 

233.  Grooving. — Internal  corrosion  and  grooving  are  often 
found  together.  Corrosion  is  sometimes  aggravated  by  slight 
local  movements  which  take  place  in  certain  parts  of  the  boiler 
and  which  are  caused  by  changes  in  pressure  or  temperature. 
These  slight  movements  loosen  particles  of  rust  as  fast  as  they 
are  formed,  thus  exposing  a  fresh  surface  for  the  formation  of  more 
rust  and  the  corrosion  from  this  cause  is  increased.  If  the 
corrosion  thus  produced  is  confined  to  a  particular  spot  instead  of 
being  spread  over  an  extended  surface  it  produces  grooving. 
Grooves  and  cracks  may  al&o  be  started  by  the  movements 
above  noted  taking  place,  often  weakening  the  metal  or  "fatigu- 
ing" it,  as  it  is  called,  until  the  metal  is  finally  split. 

Grooving  is  most  likely  to  occur  in  corners  in  such  locations 
as  where  the  head  of  a  boiler  joins  the  cylindrical  part  of  the 
shell.  In  such  cases  it  is  often  due  to  the  movement  of  the  head 


INSPECTION  AND  CARE  OF  BOILERS 


321 


from  changes  in  pressure  and  temperature,  while  the  shell  is 
stationary.  An  example  of  this  kind  of  grooving  is  shown  in 
Fig.  176.  Cases  of  grooving  like  this  may  be  prevented  by 
bracing  the  head  to  prevent  any  movement  between  it  and  the 
shell.  It  most  often  occurs  below  the  water  line,  but  is  some- 
times found  above  the  water  line  when  the  steam  space  is  small 


FIG.  176, 


FIG.  177. 


and  the  surfaces  above  the  water  line  apt  to  be  wetted  by  the 
boiler's  priming.  Sometimes  grooving  i&  found  at  the  rounded 
corners  of  locomotive  type  boilers  where  the  crown  sheet  is  bent 
over  to  meet  the  side  sheets,  as  shown  in  Fig.  177.  In  some 
cases,  also,  grooving  occurs  at  the  bottom  of  the  water  leg  in 
this  type  of  boiler,  especially  if  the  bottom  of  the  water  leg  is 
fitted  with  a  solid  mud  ring.  An  example  of  this  is  shown  in 
Fig.  178. 


FIG.  178. 


FIG.  179. 


Grooving  is  often  found  along  the  side  seams  of  boilers  which 
have  lap  joints  running  the  length  of  the  boiler,  as  shown  in  Fig. 
179.  This  is  more  often  found  in  boilers  of  small  diameter,  such 
as  small  vertical  boilers,  and  is  due  to  the  bending  which  occurs 
in  a  lapped  seam  when  under  pressure.  These  grooves  are 
never  found  where  double  strapped  butt  joints  are  used  for 
longitudinal  seams. 

234.  Patches. — Many  of  the  defects  due  to  mechanical  features 


322 


STEAM  BOILERS 


of  a  boiler  arise  from  repairs  and  may  be  largely  avoided  if  the 
repairing  is  carefully  done.  Patches  are  one  of  the  most  fruitful 
causes  of  trouble  and  often  lead  to  serious  results.  Patches  are 
often  required  where  plates  have  been  burned  or  corroded  from 
the  use  of  impure  feed  water.  When  it  is  necessary  to  apply  a 
patch,  the  defective  part  should  be  cut  away  and  not  simply 
covered  by  the  patch,  as  is  often  done.  Such  a  repair  may  be 
justified  in  some  cases  when  it  is  only  temporary,  but  it  should 
never  be  used  permanently  because  it  arouses  a  false  sense  of 
security.  Patches  should  always  be  applied  to  the  inside  of  a 
boiler  shell  if  below  the  water  line,  because,  if  placed  outside,  a 


FIG.  180. 

small  pocket  of  a  depth  equal  to  the  thickness  of  the  plate  is 
formed  inside  and  soon  fills  with  sediment,  which  causes  the 
patch  to  become  burned. 

Fig.  180  shows  a  defective  method  of  stopping  leakage  from 
a  screwed  stud  stay,  by  the  application  of  a  " cupped"  patch. 
Such  a  patch  cannot  add  strength  to  the  stay  while  it  may  conceal 
serious  weakness  and  usually  involves  more  trouble  to  apply 
than  would  a  sound  repair.  This  repair  should  have  been  made 
by  cutting  out  the  defective  plate,  placing  a  sound  patch  over 
the  portion  cut  away,  and  boring  and  tapping  a  hole  in  the  patch 
for  the  stay  to  be  screwed  into.  If  the  thread  on  the  stay  is 
defective,  then  a  new  stay  should  be  inserted.  When  patches 


INSPECTION  AND  CARE  OF  BOILERS 


323 


are  applied,  care  should  be  exercised  to  make  the  rivet  holes  in 
the  patch  come  in  line  with  those  in  the  plate.  If  they  are  not 
in  line  and  need  adjustment,  a  reamer,  and  not  a  taper  drift  pin, 
should  be  used.  Joining  together  a  thin  and  thick  plate  should 
be  avoided,  especially  if  the  joint  is  exposed  to  the  fire.  A  joint 
of  this  kind  will  be  quickly  burned. 

235.  Lap  Fractures. — Lap  fractures  are  particularly  liable  to 
occur  in  externally  fired  boilers  in  the  parts  exposed  to  the  fire, 
and  are  usually  caused  by  using  a  drift  pin  too  freely.  The 
fractures  may  extend  from  the  rivet  holes  to  the  edge  of  the 
plate,  in  which  case  they  are  not  particularly  dangerous,  unless 
too  numerous,  and  then  the  cracked  part  of  the  plate  should  be 
cut  out  and  replaced  by  a  patch.  Sometimes  these  cracks  extend 
into  the  body  of  the  plate  and  are  apt  to  grow  longer.  They  may 


0  C 

£o 

0 

9 

o 

FIG.  181. 

be  stopped  by  drilling  a  hole  at  the  end  of  the  crack  and  inserting 
a  stop  rivet  as  shown  at  A  in  Fig.  181.  Lap  fractures  are  also 
apt  to  occur  along  the  seam  and  they  may  grow  from  one  rivet 
hole  to  another  until  they  produce  a  seam  rip.  These  are  more 
dangerous  than  those  extending  to  the  edge  of  the  plate,  and 
should  receive  attention  as  soon  as  discovered. 

236.  Screwed  Stay  Repairs. — The  ends  of  screwed  stays  are 
liable  to  corrosion  and  often  need  repairing.     The  repair  should 


FIG.  182. 

be  made  by  replacing  the  stays  with  new  ones  if  the  threads  are 
corroded.  If  the  plate  is  corroded,  the  hole  should  be  bored 
larger  and  a  new  stay  of  larger  size  used.  The  enlargement  of 
stay  holes,  however,  can  easily  be  carried  too  far,  as  shown  by 
Fig.  182.  This  shows  where  adjoining  stay  holes  were  enlarged 


324  STEAM  BOILERS 

in  order  to  cut  away  the  corroded  plate,  and  enlarged  stay  ends 
were  used.  After  being  used  a  while,  the  stays  again  began  to 
leak,  and  the  leaks  were  stopped  by  inserting  smaller  screwed  pins 
at  the  edges  of  the  stays.  So  much  of  the  metal  between  the 
stays  was  removed  in  this  way  that  they  finally  gave  way  under 
the  pressure  in  the  boiler. 

237.  Hammer  Test. — Many  of  the  mechanical  defects  men- 
tioned above  may  be  detected  by  the  sound  of  a  hammer  blow 
struck  on  the  defective  part.     With  a  little  practice  of  the  ear  in 
the. sound  made  by  a  hammer  blow,  this  test  becomes  very  useful 
in  locating  defects.     It  aids  in  the  inspection  of  places  which  are 
too  inaccessible  to  be  inspected,  and  forms  a  ready  means  of 
discovering  broken  or  cracked  stays  and  bolts,  and  loose  or  slack 
rivets  or  tubes. 

238.  Hydraulic  Test. — The  hydraulic  test  is  applied  to  boilers 
to  determine  their  strength  without  running  the  risk  of  an  explo- 
sion, as  would  be  the  case  if  the  pressure  was  applied  with  steam 
or  air.     As  water  can  be  compressed  only  slightly,  a  boiler  which 
gives  way  under  water  pressure  simply  lets  the  water  run  out 
without  producing  an  explosion.     This  kind  of  test  is  practically 
always  applied  to  new  boilers  and  is  usually  one  of  the  conditions 
upon  which  they  are  bought.     The  hydraulic  test  is  used  with 
old  boilers  to  determine  if  they  are  suited  for  the  pressure  they 
are  to  carry  and  also  to  determine  their  tightness  and  the  tight- 
ness of  patches  and  other  repair  work. 

The  pressure  usually  placed  upon  a  boiler  during  an  hydraulic 
test  is  50  per  cent  more  than  the  pressure  which  the  boiler  is  to 
carry.  Thus,  if  a  boiler  is  to  carry  a  pressure  of  100  Ib.  per  sq. 
in.  it  would  be  placed  under  an  hydraulic  pressure  of  150  Ib. 
per  sq.  in.  during  the  test. 

In  order  to  perform  an  hydraulic  test  on  a  boiler,  it  is  entirely 
filled  with  cold  water  and  a  small  hand  pump  attached  to  some 
fitting  in  order  to  place  the  water  under  pressure.  While  the 
boiler  is  being  filled,  some  part  of  it  near  the  top  should  be  opened 
in  order  to  let  the  air  out,  as  this  would  collect  on  top  of  the  water 
and  be  compressed.  If  a  boiler  should  give  way  while  it  contains 
compressed  air,  there  is  apt  to  be  an  explosion  from  the  energy 
stored  in  the  compressed  air.  As  the  water  used  in  filling  the 
boiler  will  contain  a  little  air,  a  few  extra  strokes  of  the  pump 
will  be  necessary  after  the  boiler  is  filled,  in  order  to  put  it  under 
pressure.  Warm  water  should  not  be  used  in  filling  the  boiler 


INSPECTION  AND  CARE  OF  BOILERS 


325 


as  small  leaks  are  difficult  to  detect  with  it,  owing  to  the  evapora- 
tion of  the  water  as  fast  as  it  passes  through  the  leak.  It  is 
usual  to  maintain  the  hydraulic  pressure  for  about  half  an  hour 
after  being  applied,  and  to  give  the  boiler  a  careful  examination 
ior  leaks  and  bulges  during  this  time. 

239.  Defective  Fittings. — Fittings  may  be  defective  in  a  great 
many  ways,  but  space  permits  of  only  a  few  being  mentioned  here. 


FIG.  183. 


FIG.  184. 

The  fittings  most  commonly  found  defective  are  gage  glasses, 
blow-off  valves,  safety  valves,  and  steam  gages.  Trouble  is 
often  experienced  with  a  gage  glass  from  the  stoppage  of  the 
passages  leading  from  the  boiler  to  the  glass,  causing  the  gage  to 
indicate  a  false  water  line.  Stoppage  of  these  passages  may  be 
due  to  deposits  of  mud  or  sediment  from  impure  feed  water,  or 
to  the  lack  of  a  recess  for  the  glass  tube  packing  as  shown  in  Fig. 
183,  whereby  the  packing  may  be  squeezed  under  the  end  of  the 
tube  when  the  follower  nut  is  screwed  down. 


326  STEAM  BOILERS 

The  most  common  defect  with  blow-off  valves  is  leakage  of 
water  past  the  valve,  which  may  quickly  result  in  a  dangerous 
condition  of  low  water.  Only  the  best  types  of  valve  should  be 
used  on  the  blow-off,  and  the  use  of  two  of  them  is  an  advantage. 
Each  time  the  boiler  is  emptied,  the  blow-off  valves  should  be 
taken  apart  and  examined  for  defects.  When  a  globe  valve  is 
used  in  the  blow-off,  it  sometimes  happens  that  the  valve  is  set 
with  the  wrong  end  toward  the  boiler,  which  allows  sediment  to 
collect  under  it  until  it  becomes  choked,  as  illustrated  in  Fig.  184. 
This  valve  should  be  set  so  the  boiler  pressure  will  act  on  top  of 
the  disc. 

Safety  valves  are  a  fruitful  source  of  trouble  and  require 
careful  watching  to  keep  them  in  good  condition.  The  stems  of 
lever  safety  valves  are  apt  to  stick  or  become  rusted  where  they 
pass  through  the  casing  or,  if  there  is  packing  at  this  point,  the 
follower  nut  may  be  screwed  down  too  tightly,  causing  the 
packing  to  grip  the  stem  and  thus  hold  the  valve.  Spring 
safety  valves  are  less  liable  to  defects,  but  sometimes  the  stems 
of  these  become  rusted  or,  if  of  the  outside  spring  type,  the 
springs  may  be  screwed  down  too  tightly. 

Steam  gages  often  read  wrong  after  being  in  use  awhile,  due  to 
wear  or  slipping  of  the  mechanism,  and  for  this  reason  they 
should  be  tested  from  time  to  time  and  the  pointer  reset  to  in- 
dicate correctly.  Injury  sometimes  results  from  the  use  of  a 
defective  steam  gage  by  opening  the  boiler  too  soon,  there  being 
pressure  in  the  boiler  even  though  the  pointer  stands  at  zero. 
Before  a  boiler  is  opened,  the  safety  valve  should  always  be 
lifted  if  the  boiler  has  been  under  pressure  a  short  while  before. 

240.  Care  of  Boilers. — While  no  two  boilers  are  exactly  alike, 
each  having  a  sort  of  individuality  of  its  own,  and  requiring  a 
little   different  treatment  than  others,   yet  there   are   certain 
general  rules  regarding  the  care  of  boilers  which  apply  in  all 
cases.     By  observing  these  rules,  the  safety,  economy,  and  life 
of  the  boiler  may  be  greatly  increased,  and  the  plant  kept  in 
better  condition  and  handled  with  more  ease  than  will  be  the 
case  if  the  rules  are  not  regarded.     Most  of  these  rules  are  to  be 
found   in   the   Engineer's   Manual  issued  by  the  Fidelity  and 
Casualty  Insurance  Company. 

241.  Safety  Valves. — These  valves  should  be  of  ample  size  and 
kept  in  working  order.     The  valves  should  be  tried  daily;  this 
is  best  done  by  allowing  the  pressure  to  rise  gradually  until  the 


INSPECTION  AND  CARE  OF  BOILERS  327 

valves  just  "  simmer, "  noting  the  pressure  by  the  steam  gage  at 
the  moment.  Freedom  of  action  may,  of  course,  be  ascertained 
by  hand,  but  it  cannot  be  known  by  this  means  that  the  valve 
will  blow  off  when  the  proper  pressure  is  attained.  Neglect  and 
overloading  of  this  most  important  adjunct  are  prolific  causes  of 
boiler  explosions.  Each  boiler  should  have  its  own  safety  valve 
and  no  stop  valve  should  be  permitted  between  it  and  the 
boiler. 

242.  Pressure    Gage. — It    is    absolutely    necessary   that    the 
pressure  gage  should  be  trustworthy  and  if  there  is  any  reason  to 
question  its  readings,  it  should  be  compared  with  one  known  to 
be  accurate.     The  gage  should  be  fitted  to  a  "loop"  filled  with 
water,  which  transmits  the  pressure  and  prevents  contact  of 
steam  with  the  gage  spring.     Attach  the  gage  directly  to  the 
boiler  and  not  to  a  steam  pipe,  to  prevent  fluctuations  of  pressure 
readings. 

243.  Water  Level. — Before  starting,  make  sure  that  there  is 
plenty  of  water  in  the  boiler  by  trying  the  gage  cocks.     While 
running,  do  not  depend  on  the  gage  glass  but  try  the  gage  cocks 
often.     The  water  line  should  be  kept  at  a  regular  height,  and 
should  never  be  less  than  3  or  4  in.  above  the  fire  line,  or  above 
the  top  row  of  tubes  in  a  return  fire-tube  boiler.     The  gage  glass 
should  be  blown  out  frequently  to  see  that  it  is  not  choked.     It 
is  an  excellent  plan  to  try  the  gage  cocks  every  15  minutes. 
Both  the  gage  glass  and  cocks  must  be  kept  clean. 

244.  Dampers. — Do  not  close  the  damper  entirely  while  there  is 
fire  on  the  grates,  as  gas  may  collect  in  the  tubes  and  cause  a 
serious  explosion.     Make  liberal  use  of  the  damper  in  regulating 
the  generation  of  steam.     Remember  that  steam  going  out  of 
the  safety  valve  means  money  lost. 

245.  Feed  Pump  or  Injector. — These  should  be  kept  in  order 
and  should  be  of  ample  size  for  all  requirements.     The  feed  pump, 
however,  ought  not  to  be  so  large  as  to  render  it  difficult  to  feed 
the  boiler  continuously  at  a  slow  rate  of  speed.     It  is  always 
safer  to  have  two  means  of  feeding.     An  injector  should  be  used 
when  no  feed  water  heater  is  provided,  as  it  prevents  the  contrac- 
tion of  tubes  and  plates  where  the  feed  water  comes  in  contact 
with  them. 

246.  Low   Water. — The  blow-out  apparatus  should  be  kept 
tight,  as  any  leakage  here  may  cause  low  water,  with  the  result 
of  overheating  the  plates.     In  case  of  low  water,  fresh  coal,  or, 


328  STEAM  BOILERS 

better  still,  wet  ashes,  must  be  thrown  on  the  fire  at  once. 
Do  not  turn  on  the  feed  (though,  if  already  in  motion,  allow  it  to 
continue),  or  start  or  stop  the  engine,  or  lift  the  safety  valve,  until 
the  boiler  has  cooled  down.  After  a  case  of  low  water,  the  tube 
ends  in  the  upper  rows  should  be  examined  for  leaks. 

247.  Incrustation  and  Corrosion. — Boilers  should  be  kept  free 
from  scale,  as  its  presence  increases  the  liability  of  burning  or 
cracking  the  plates   and  may  lead  to  explosions.     The  surest 
method  of  preventing  internal  corrosion  is  to  abandon  the  use 
of  the  water  which  causes  it,  but  if  this  is  impracticable  the  water 
should  be  treated  and  a  sharp  lookout  should  be  kept  for  de- 
fects.    Leaks  at  seams  and  fittings,  drippings  from  pipes,  ex- 
posure to  the  weather,  contact  of  the  boiler  with  brick-work,  etc., 
are  causes  of  external  corrosion  and  should  be  remedied  at  once. 

248.  Galvanic  Action. — Sometimes  boilers  may  be  protected 
by  means  of  zinc  from  the  action  of  corrosive  agents  present 
in  the  water.     As  a  rule  1  sq.  ft.  of  surface  of  zinc  to  every  50 
sq.  ft.  of  heating  surface  in  the  boiler  is  sufficient.     The  plate's 
should  be  placed  in  perfect  metallic  contact  with  the  iron  and 
renewed  as  they  are  wasted. 

249.  Blisters,  Cracks,  and  Burnt  Plates. — When  these  occur 
they  should  receive  attention  at  once.     Burnt  places  and  blisters 
should  be  cut  out  and  a  patch  put  on  the  inside  of  the  boiler  to 
avoid  making  a  pocket  for  the  collection  of  sediment.     Bags 
should  be  repaired  immediately.     If  not  down  too  far  and  the 
metal  is  sound,  they  can  sometimes  be  driven  back;  otherwise  it 
will  be  necessary  to  cut  them  out  and  patch. 

250.  Fusible  Plugs. — These  are  required  by  law  in  some  states. 
To  keep  them  in  efficient  condition  their  surfaces,  both  on  the  fire 
and  water  sides,  must  be  often  scraped  clean,  but  notwithstanding 
all  precautions,  they  are  unreliable. 

251.  Covering. — Radiation  from  the  dome  and  the  top  of  the 
boiler  is  a  source  of  waste.     A  covering  of  asbestos  or  other 
suitable    non-conducting    material    should    be    provided    as   a 
protection. 

252.  Green   Walls. — Firing    a    boiler   with    green   walls    will 
invariably  crack  the  setting,  hence,  it  is  absolutely  necessary  to 
dry  out  the  brick  work  properly.     If  circumstances  permit,  it  is 
advisable  as  soon  as  stack  connections  are  made,  to  block  open 
the  ash  pit  doors  and  the  damper  so  that  circulation  of  air  will 
aid  in  drying  the  brick  work.     The  next  step  is  to  fill  the  boiler 


INSPECTION  AND  CARE  OF  BOILERS  329 

with  water  and  put  in  a  light  fire  of  shavings,  which  may  grad- 
ually be  increased  by  using  some  wood,  continuing  until  the 
walls  are  thoroughly  dried  inside  and  out.  This  will  require 
several  days,  but  by  close  observation,  the  walls,  if  carefully 
built,  can  be  dried  out  without  cracking. 

When  steam  is  available,  an  excellent  method  of  drying  the 
brick  work  is  to  connect,  temporarily,  a  small  steam  supply  pipe 
to  the  new  boiler,  and  to  attach  a  trap  or  other  drainage  apparatus 
to  the  blow-off  pipe.  The  new  boiler,  when  filled  with  steam,  will 
act  as  a  radiator  and  will  heat  the  air  around  it;  hence,  if  ash-pit 
doors  and  damper  be  left  open,  there  will  be  a  steady  current  of 
warm  air  passing  through  the  setting  and  the  brickwork  will  be 
gradually  and  effectively  dried.  The  steam  supply  should  be 
very  small  at  first  and  be  increased  as  the  drying-out  proceeds. 

253.  Cutting  Boiler  into  Steam  Main. — Under  no  circumstances 
whatever  should  a  boiler  be  "  cut-in"  with  other  boilers  unless  the 
pressure  within  it  is  identical  with  that  in  the  main.     Before  open- 
ing the  boiler  stop  valve  or  header  valve,  be  sure  that  there  is  no 
water  in  the  length  of  pipe  between  these  two  valves.     Steam 
valves  should  always  be  opened  or  closed  very  slowly  and  the 
valves  should  first  be  eased  from  their  seats  slightly  for  some 
moments  to  permit  a  circulation  to  become  established  before 
valves  are  fully  opened. 

254.  Starting  the  Engine. — Engines  should  be  started  slowly 
in  order  not  to  make  a  violent  change  in  the  condition  of  the  water 
and  steam  in  the  boiler  and,  when  possible,  the  engine  should  be 
stopped  gradually.     The  sudden  opening  of  a  large  stop-valve 
may  produce  a  violent  rush  of  steam  and  water  against  that  part 
of  the  boiler  whence  the  steam  is  drawn,  the  percussion  of  which 
may  be  sufficient  to  rupture  the  boiler. 

255.  Firing.— The  fire  should  be  kept  level  and  of  somewhat 
greater  thickness  at  the  bridge  wall.     This  promotes  a  uniform 
consumption  of  fuel,  as  the  air  passes  more  freely  through  the 
fire  near  the  bridge  wall  and  the  greater  thickness  retards  its 
passage.     Fuel  supplied  regularly  in  small  quantities,  combined 
with   an  even  distribution,   produces  the  best  results.     When 
anthracite  coal  is  used,  the  average  thickness  of  the  fire  should 
be  6  to  8  in. ;  with  bituminous  coal  it  should  be  8  to  10  in. ;  with 
coke  10  to  12  in.     If  the  draft  is  poor,  however,  a  thin  fire  must 
be  used.     Do  not  fire  with  large  lumps.     No  fragment  should  be 
larger  than  a  man's  fist. 


330  STEAM  BOILERS 

Complete  combustion  is  attained  only  when  the  fuel  is  burning 
with  a  bright  flame  all  over  the  grate.  Blue  flames,  dark  spots, 
and  smoke  are  evidences  of  the  lack  of  the  necessary  air  which 
ought  to  be  supplied  above  the  grate.  Fires  should  be  "  cleaned  " 
no  oftener  than  necessary.  In  using  a  caking  coal  it  is  advan- 
tageous to  make  use  of  a  " coking  fire";  i.e.,  firing  in  front, 
breaking  up  with  a  slice  bar,  and  shoving  back  when  coked.  The 
practice  of  wetting  coal  before  throwing  it  on  the  fire  is  a  bad  one, 
as  it  wastes  heat  and  promotes  corrosion. 

256.  Banking  Fires. — Contraction  and  expansion,  caused  by 
change  of  temperature,  shorten  the  life  of  a  boiler.     For  this 
reason  it  is  better  to  bank  the  fires  at  night  instead  of  drawing 
them. 

257.  Rapid  Firing. — Steam  should  be  raised  slowly  in  a  boiler 
having  thick  plates  or  seams  exposed  to  the  fire,  else  overheating 
or  burning  will  result.     The  greatest  effect  of  the  fire  on  a  boiler 
bottom  takes  place  immediately  behind  the  bridge  wall,  and,  if  a 
seam  is  located  at  this  point,  there  is  liability  of  burning  the  lap. 
It  is  best  in  such  cases  to  change  the  position  of  the  bridge,  so  the 
seam  comes  over  the  bridge,  or  better  still,  over  the  furnace. 

258.  Feeding. — Wear  and  tear  of  a  boiler,  arising  from  unequal 
expansion  and  contraction,  is  increased  by  allowing  the  feed  water 
to  enter  at  too  low  a  temperature.     If  the  use  of  cold  water  is 
unavoidable,  the  feed  pipe  should  always  be  extended  well  into 
the  interior  of  the  boiler  and  should  enter  horizontally  through 
the  front  head  near  one  side,  and  a  few  inches  below  the  water 
line.     By  this  means  the  feed  water  is  heated  nearly  to  the  tem- 
perature of  the  water  in  the  boiler,  and  is  discharged  at  the  cool- 
est part  of  the  boiler.     The  use  of  an  injector  or  feed-water  heater 
renders  this  extension  of  the  feed  pipe  unnecessary. 

259.  Foaming. — In  case  of  foaming,  close  the  throttle  and  open 
the  fire  doors  for  a  few  minutes,  when  the  water  will  usually 
settle  and  its  height  may  be  determined.     The  trouble,  if  caused 
by  dirty  water,  can  easily  be  overcome  by  feeding  and  blowing. 
Where  there  is  a  surface  blow  it  can  be  used  to  good  advantage. 

260.  Blowing  Out. — The  bottom  blow-off  cock  should  be  kept 
tight  to  prevent  loss  by  leakage.     A  plug  cock  is  the  simplest, 
surest,  and  most  durable  valve  for  this  purpose.     When  the  feed 
water  is  of  a  hard  or  muddy  nature  the  boiler  should  be  blown  out 
frequently.     A  boiler  should  never  be  emptied  while  the  brick- 
work is  hot,  as  this  will  bake  the  sediment  on  the  plates  and  make 


INSPECTION  AND  CARE  OF  BOILERS  331 

its  removal  difficult.  A  boiler  should  be  emptied  every  week  or 
two,  and  filled  afresh.  The  blow-off  valve  should  be  opened  wide 
for  a  moment  each  day.  This  will  aid  in  keeping  boiler  and  blow- 
off  pipe  clear.  Never  open  the  blow-off  valve  or  cock  with  a 
jerk,  as  it  is  liable  to  let  go  and  cause  a  serious  accident.  Do  not 
blow  off  under  pressure  when  intending  to  clean  boilers,  as  the 
heat  of  the  boiler  and  brickwork  will  bake  the  mud  and  scale  on 
the  shell  and  tubes,  making  it  extremely  difficult  to  remove.  The 
proper  manner  to  use  a  surface  blow-off  is  to  open  it  for  about 
fifteen  seconds  every  hour  rather  than  for  a  longer  time  at  greater 
intervals. 

261.  Feed  Water  Heating. — Heating  the  feed  water,  either  by 
means  of  exhaust  steam  or  the  waste  gases  in  the  chimney,  adds 
to  the  economy  of  a  steam  plant.     Each  increase  in  the  tempera- 
ture of  the  feed  water  of  10°  F.  means  a  saving  of  fuel  of  1  per 
cent.     No  saving  in  fuel  is  effected  by  the  use  of  an  injector,  but 
the  employment  of  one  promotes  the  longevity  of  a  boiler  by 
introducing  the  feed  water  at  a  temperature  so  high  that  no 
injurious   contractions  are   caused  in  any  part  of  the  boiler. 

262.  Cleaning. — The  heating  surfaces  of  a  boiler,  both  inside 
and  out,  should  be  kept  clean,  in  order  to  prevent  a  serious  waste 
of  fuel.     The  thickness  of  the  soot  or  scale  which  is  allowed  to 
accumulate  ought  never  to  exceed  1/16  in.     After  allowing  the 
boiler  and  brickwork  to  cool,  the  boiler  should  then  be  drained 
and  thoroughly  cleaned  and  washed  out  both  from  the  top  and 
bottom. 

263.  Leaks  in  Brickwork. — Cracks  or  openings  in  the  brick- 
work should  be  carefully  stopped.     The  admission  of  air,  except 
at  the  places  provided  for  it,  impairs  the  draft,  cools  the  gases 
on  their  way  to  the  tubes,  and  sometimes  causes  jets  of  flame  to 
impinge  so  strongly  on  the  shell  as  to  injure  the  plates. 

264.  Moisture. — The  exterior  of  a  boiler  should  be  protected 
from  moisture,  as  it  brings  about  corrosion  and  consequent  weak- 
ening of  the  boiler. 

265.  Disuse  of  Boilers. — If  a  boiler  remains  idle,  it  will  deter- 
iorate much  faster  than  when  in  use,  unless  it  receives  proper  atten- 
tion as  soon  as  its  use  is  discontinued.     Hence,  the  following 
instructions  should  be  carefully  observed.     Before  emptying  the 
boiler,  place  in  the  shell  or  steam  drum  several  gallons  of  crude 
oil  so  that  when  the  blow-off  is  opened  the  oil  will  form  a  light 
covering  over  the  tubes  and  inside  surfaces  of  the  shell.     Before 


332  STEAM  BOILERS 

the  boiler  is  used  again  this  oil  must  be  removed  with  soda  ash. 
Dry  the  boiler  thoroughly  when  emptied.  If  the  boiler  cannot  be 
emptied,  fill  it  completely  with  water  to  which  has  been  added  a 
quantity  of  soda-ash,  then  boil  off  the  air  and  close  the  boiler 
air  tight.  Clean  off  all  accumulations  of  ash  and  soot  with  a 
scraper  or  wire  brush  and  give  the  exterior  of  all  tube  and  shell 
surfaces  a  coat  of  boiled  linseed  oil.  Smear  all  brass  or  finished 
work  with  vaseline  slush  or  a  mixture  of  white  lead  and  tallow. 
Cover  the  stack  tops  with  a  water-tight  hood  and  see  that  no 
water  can  reach  the  boiler  through  breechings,  openings  in  roof, 
or  other  sources. 


CHAPTER  XX 
BOILER  TESTING 

266.  Object  of  Tests.— Besides  the  tests  described  in  the  preced- 
ing chapter  for  determining  the  physical  condition  of  a  boiler, 
its  strength  and  ability  to  carry  a  certain  pressure,  other  tests  are 
often  made  to  determine  its  efficiency  and  power.     Such  tests  are 
often  called  " evaporative  tests,"  since  the  more  water  a  boiler 
will  evaporate  the  greater  will  be  its  power  and  the  efficiency 
depends   upon  the  amount  of  water  evaporated  with  a  certain 
amount  of  fuel. 

267.  Methods  of  Testing  Boilers. — The  simplest  form  of  boiler 
test  consists  in  weighing  each  day  the  coal  used  and  the  water  fed 
to  the  boiler.     Some  boiler  plants  are  provided  with  weighing 
apparatus  for  this  purpose  and  the  fireman  is  able  to  keep  a 
record  of  the  performance  of  the  boiler.     However,  such  a  test 
as  this  gives  only  approximate  results  as  there  are  many  features 
about  the  operation  of  a  boiler  which  vary  from  day  to  day  and 
which  would  change  the  results  if  they  were  taken  into  account. 
Some  of  these  variable  features  are:  the  load;  the  quality  of  the 
steam  produced  by  the  boiler;  the  heating  value  of  the  coal  used; 
the  amount  of  unburned  coal  dropping  through  the  grates;  and 
the  temperature  of  the  feed  water. 

In  order  to  obtain  accurate  and  full  results  from  a  boiler  test, 
and  to  arrange  such  results  so  that  one  boiler  may  be  compared 
with  another,  even  though  they  are  located  at  different  places  and 
are  operated  under  entirely  different  conditions,  engineers  have 
agreed  upon  a  standard  method  of  testing,  and  of  computing 
results,  and  a  standard  form  for  reporting  the  results  of 
tests. 

In  order  to  make  a  test  of  this  kind,  it  is  necessary  to  weigh  the 
water  fed  to  the  boiler  during  the  time  of  the  test  and  obtain  its 
temperature,  to  weigh  the  coal  fired  during  the  test  and  obtain 
an  average  sample  of  it  to  be  analyzed  later,  to  weigh  the  ashes  and 
refuse  taken  out  of  the  ash  pit  during  the  test,  to  read  the  steam 

333 


334  STEAM  BOILERS 

pressure  at  frequent  intervals,  and  to  measure  the  quality  of  the 
steam  delivered  by  the  boiler.  Other  data  which  it  is  advisable 
to  take  if  possible  to  do  so,  but  which  are  not  necessary  for  the 
calculations,  are:  force  of  draft  in  the  furnace  and  between  the 
damper  and  the  boiler;  temperature  of  the  gases  leaving  the 
boiler,  and  the  analysis  of  the  flue  gas. 

A  boiler  test  should  extend  for  24  hours  in  order  to  obtain 
good  average  results.  If  it  is  impossible  to  do  this,  the  test  may 
last  for  12  hours,  but  should  not  be  conducted  for  less  than  10  hours 
in  any  case.  If  the  test  is  made  in  less  than  10  hours  there  is  apt 
to  be  serious  error  in  obtaining  the  weight  of  ash  and  this  will 
affect  the  computed  results  to  such  an  extent  as  to  make  them  of 
little  value. 

268.  Observations. — The    two     principal     quantities    to    be 
determined  by  a  boiler  test  are  the  number  of  pounds  of  water 
evaporated  by  the  boiler  and  the  number  of  pounds  of  fuel 
necessary  to  evaporate  it.     In  order  to  determine  these  two 
quantities  it  is  necessary  to  weigh  the  feed  water  fed  into  the 
boiler  and  the  coal  fed  into  the  furnace.     The  greatest  care  should 
be  exercised  in  taking  these  weights  because  any  error  in  them 
affects  directly  the  results  of  the  test. 

269.  Weighing  the  Coal. — A  good  method  of  handling  and 
weighing  the  coal  is  to  fill  a  barrow  or  car  which  holds  about 
500  lb.;  and  weigh  both  the  car  and  coal  on  a  platform  scales 
placed  in  front  of  the  furnace.     The  furnace  should  be  fired 
directly  from  the  car  which  should  be  weighed  again  after  firing. 
The  difference  between  this  and  the  first  weight  will  be  the  weight 
of  coal  fired.     When  all  the  coal  in  the  car  has  been  fired,  the  car 
itself  is  weighed.     The  time  of  taking  these  weights  together 
with  the  weights  themselves  are  recorded  on  a  sheet  of  paper 
ruled  especially  for  this  purpose.     This  sheet  of  paper  containing 
the  date  is  called  the  log.     The  reason  for  arranging  the  log  in 
this  way,  is  so  that  any  error  may  be  detected,  since  the  sum  of  the 
separate  charges  must  be  equal  to  the  difference  between  the 
sums  of  the  weights  of  the  car  when  filled  and  when  empty. 

270.  Sampling  the  Coal. — From  each  car  of  coal  should  be 
taken  a  small  shovelful  to  be  used  as  a  sample.     The  sample 
should  be  taken  before  the  coal  is  weighed,  and  it  should  be 
stored  away  in  a  cool  place  until  the  end  of  the  test.     At  the  end 
of  the  test,  all  the  samples  taken  should  be  thoroughly  mixed  and 
the  lumps  broken  into  pieces  about  the  size  of  pea  coal.     The 


BOILER  TESTING 


335 


sample  of  coal  should  then  be  spread  out  and  divided  into  quarters. 
One  of  the  quarters  should  be  retained  and  again  mixed  and 
quartered,  and  this  process  should  continue  until  the  sample 
consists  of  about  enough  to  fill  a  quart  fruit  jar.  This  final 
sample  should  then  be  sealed  in  an  air-tight  jar  to  prevent  loss 
of  moisture,  and  sent  to  a  chemist  for  proximate  analysis  and 
determination  of  heating  value. 

271.  Weighing  Water. — The  water  may  be  conveniently 
weighed  by  means  of  two  tanks  as  shown  in  Fig.  185.  Two  tanks 
are  arranged  one  above  the  other,  the  top  one  resting  on  platform 


_  Weighing  and 
Measuring  Tank 


FlG.    185. 

scales.  The  upper  tank  is  used  for  weighing  the  water,  after 
which  it  is  allowed  to  flow  into  the  lower  tank  and  is  fed  from 
there  directly  into  the  boiler.  The  supply  of  feed  water  is  led 
by  a  pipe  of  generous  size  to  a  point  directly  above  the  upper 
tank  so  the  tank  may  be  filled  quickly.  This  tank  has  a  conical 
bottom,  so  that  all  the  water  will  run  out  at  each  emptying.  The 
discharge  pipe,  which  should  be  about  3-in.  in  diameter,  is  con- 
nected to  the  center  of  the  bottom  and  is  fitted  with  a  quick  open- 
ing valve  or  cock  so  that  the  tank  may  be  emptied  quickly.  The 
upper  tank  has  an  overflow  so  that  it  may  be  filled  to  the  same 

28 


336  STEAM  BOILERS 

height  each  time.  Instead  of  an  overflow,  the  tank  may  be  marked 
at  a  certain  height  and  filled  to  this  mark  each  time.  If,  before 
the  test  is  started,  the  upper  tank  is  filled  to  the  mark  and  the 
water  weighed,  filling  it  to  this  mark  each  time  serve?  as  a  check 
on  the  weighing.  The  bottom  tank  should  be  somewhat  larger 
than  the  upper  one.  The  suction  of  the  feed  pump  or  injector  is 
placed  in  the  lower  tank  and  ends  near  its  bottom.  The  feed- 
water  temperature  may  be  taken  by  placing  a  thermometer  in 
this  tank. 

In  operation,  the  upper  tank  is  filled  and  weighed  and  then 
emptied  into  the  lower  one.  While  the  water  is  being  fed  into 
the  boiler  from  the  lower  tank  the  upper  one  is  again  filled  and 
weighed.  If  the  amount  of  water  fed  into  the  boiler  is  very 
large,  two  weighing  tanks  emptying  into  one  lower  tank  will  be 
an  advantage.  One  of  the  weighing  tanks  may  then  be  filled 
and  weighed  while  the  other  is  emptying. 

272.  Ash. — The  time  of  cleaning  fires  and  the  weight  of  ash 
removed  from  the  ash  pit  each  time  should  be  recorded,  and  a 
sample   of  the   ash   preserved  for   analysis,   in  order  that  the 
amount  of  unburned  coal  in  it  may  be  determined.     The  ashes 
should  be  kept  dry,  as  any  moisture  in  them  would  be  weighed 
and  make  their  weight  appear  greater  than  it  should  be. 

Although  the  principal  data  is  that  relating  to  the  feed  water 
and  coal,  the  other  data  should  be  taken  just  as  carefully,  and 
recorded.  The  readings  of  steam  pressure,  feed-water  tempei- 
ature,  and  calorimeter  temperature  and  pressure  should  be  taken 
at  the  same  instant.  It  is  especially  important  to  secure  the 
readings  of  gage  pressure,  calorimeter  pressure,  and  calorimeter 
temperature  at  the  same  time. 

273.  Starting  and  Stopping  the  Test. — There  are  two  standard 
methods  of  starting  and  stopping  a  boiler  test,  called  the  standard 
method  and  the  alternate  method.     The  alternate  method  is  the 
one  more  commonly  used  and  is  recommended  as  being  conven- 
ient and  accurate. 

274.  Standard   Method. — Steam   having   been   raised   to   the 
working  pressure,  remove  rapidly  all  fire  from  the  grates,  close 
the  damper  and  clean  the  ash  pit,  and  as  quickly  as  possible  start 
a  new  fire  with  weighed  wood  and  coal,  noting  the  time  and  also 
the  water  level  in  the  gage  glass  while  the  water  is  quiet,  just 
before  lighting  the  fire.     The  height  of  the  water  level  in  the 
gage  glass  should  be  marked  so  the  water  may  be  brought  back 


BOILER  TESTING  337 

to  the  same  level  at  the  end  of  the  test.  At  the  end  of  the  test 
remove  the  whole  fire,  which  has  been  burned  low,  clean  the 
grates  and  ash  pit,  and  note  the  water  level  when  the  water  is 
quiet,  and  record  the  time  at  which  the  fire  is  hauled.  The 
water  should  be  as  nearly  as  possible  at  the  same  height  as  at 
the  beginning  of  the  test.  If  it  is  not  the  same,  a  correction 
should  be  made  by  adding,  to  the  weight  of  water  pumped  into 
the  boiler,  an  amount  sufficient  to  bring  the  water  back  to  its 
oiiginal  height;  this  weight  also  may  be  calculated. 

275.  Alternate  Method. — While  the  boiler  is  being  operated, 
the  fires  are  to  be  burned  low  and  well  cleaned.     Note  the  amount 
of  coal  left  on  the  grate  as  nearly  as  it  can  be  estimated;  note  the 
pressure  of  steam  and  the  water  level.     This  time  should  be 
noted  as  the  starting  time,  immediately  fresh  coal  should  be 
fired,  and,  if  necessary,  more  water  fed  into  the  boiler.     The  ash 
pit  should  be  thoroughly  cleaned  immediately  after  starting. 
Before  the  end  of  the  test  the  fires  should  be  burned  low  and 
cleaned  in  such  manner  as  to  leave  the  coal  on  the  grates  in  the 
same  condition  and  of  the  same  depth  as  at  the  start.     When 
this  condition  is  secured,  note  the  time  and  record  it  as  the  stop- 
ping time.     The  water  level  and  steam  pressure  should  pre- 
viously be  brought  as  nearly  as  possible  to  the  same  point  as  at 
the  start. 

When  starting  and  stopping  a  boiler  test,  great  care  must  be 
exercised  in  reading  the  water  level,  as  it  is  easily  affected  by  the 
condition  of  the  fire.  The  water  level  should  be  read  immedi- 
ately after  cleaning  the  fire  and  when  the  boiling  is  least  violent. 
If  the  fire  is  burning  brightly,  the  water  will  boil  violently  and 
thus  raise  the  water  level.  Another  necessary  precaution  is  to 
see  that  the  fire  contains  the  same  amount  of  ash  at  the  end  as 
at  the  beginning  of  the  test.  A  small  error  in  the  weight  of  the 
ash  makes  a  large  percentage  of  error,  since  the  total  weight  of 
ash  is  small. 

276.  Results. — The  method  of  calculating  results  can  best  be 
shown  by  an  example.     In  the  example  which  follows  is  shown 
a  good  form  on  which  to  record  results.     This  form  is  shown 
filled  in  with  both  the  data  which  would  be  taken  during  the  test 
and  the  calculated  results,  the  data  being  printed  in  Roman,  and 
the  calculated  results  in  bold  face  type.     Following  the  report 
is  found  the  method  of  working  out  the  calculated  results,  the 
items  being  numbered  to  correspond  with  those  in  the  report. 


338  STEAM  BOILERS 

DATA  AND  RESULTS  OF  EVAPOKATION  TEST 
Made  by  /.  H.  Smith  of  Milwaukee,  Wis. 

Type  of  boiler  Aultman  &  Taylor  water-tube  (B.  &  W.  Type).     Located  at 
Milwaukee,  Wis. 

Purpose  of  Test        To  determine  efficiency 
Kind  of  Fuel  Bituminous 

Kind  of  Furnace        Roney  stoker 

1.  Date  of  test        March  G,  1912. 

2.  Duration  of  test 20    hours 

DIMENSIONS 

3.  Grate  surface.     Width  10  ft.     Length  6  ft. 

Area 60    sq.  ft. 

4.  Water  heating  surface 2500    sq.  ft. 

5.  No.  of  tubes Diameter  4  in.     Length.  . 

AVERAGE  PRESSURES 

6.  Barometer 28.5  in.  of  mercury 14.0  Ib.  per  sq.  in. 

7.  Steam  gage 95.7  Ib.  per  sq.  in. 

8.  Absolute  steam  pressure 109.7  Ib.  per  sq.  in. 

9.  In  calorimeter 1.8  in.  of  mercury 

10.  Draft  between  damper  and  boiler 0.37  in.  of  water. 

AVERAGE  TEMPERATURES 

11.  Escaping  gases 415  degrees 

12.  Feed  water  entering  boiler 172  degrees 

13.  Inside  calorimeter 268  degrees 

FUEL 

14.  Where  mined Carterville,  III. 

15.  Size  and  condition Pea,  No.  3 

16.  Fixed  carbon  60          per  cent 

17.  Volatile  matter 28.22  per  cent 

18.  Moisture 4.2  per  cent 

19.  Ash 7.58  per  cent 

20.  B.t.u.  per  pound  of  dry  coal 12,300  B.t.u. 

21.  B.t.u.  per  pound  of  combustible 13,360  B.t.u. 

22.  Weight  of  coal  as  fired 32,200  Ib. 

23.  Weight  of  dry  coal  fired 30,850  Ib. 

24.  Weight  of  ash  and  refuse 2870  Ib. 

25.  Per  cent  of  combustible  in  ash •.  15  per  cent 

26.  WTeight  of  combustible  burned  on  the  grates .  .  27,980  Ib. 

27.  Dry  coal  fired  per  hour 1543  Ib. 

28.  Dry  coal  fired  per  square  foot  of  grate  surface 

per  hour 25.7      Ib. 


BOILER  TESTING  339 

29.  Combustible  burned  on  grates  per  hour 1399          Ib. 

30.  Combustible  burned  on  grate  per  square  foot 

grate  surface  per  hour 23.3  .      Ib. 

31.  CO2 Per  cent  of  volume 8.0 

32.  O2    Per  cent  of  volume 9.9 

33.  CO Per  cent  of  volume .2 

34.  Total Per  cent  of  volume .  18.1 

QUALITY  OF  STEAM 

35.  Quality  of  steam 98.2        per  cent 

36.  Superheat 0        degrees 

WATER 

37.  Total  weight  of  water  fed  to  boiler 250,500          Ib. 

38.  Water    actually    evaporated,    corrected    for 

quality  of  steam  and  for  moisture 246,700          Ib. 

39.  Factor  of  evaporation 1.082 

40.  Equivalent  water  evaporated  into  dry  steam 

from  and  at  212° 267,000          Ib. 

WATER  PER  HOUR 

41.  Water   evaporated   per   hour,    corrected   for 

quality  of  steam 123,330          Ib. 

42.  Equivalent  evaporation  into  dry  steam  per 

hour  from  and  at  212° ;       13,350          Ib. 

43.  Equivalent  evaporation  per  hour  from  and  at 

212°  per  square  foot  of  heating  surface. . .  .  5.34     Ib. 

44.  Horse-power  developed 387          h.p. 

45.  Builders  rated  horse-power  on  basis  of  10  sq. 

ft.  per  horse-power 250         h.p. 

46.  Percentage    of    builders'    rated    horse-power 

developed 154.8      per  cent 

ECONOMIC  RESULTS 

47.  Water  apparently  evaporated  under  actual 

conditions  per  pound  of  coal  as  fired 7.78     Ib. 

48.  Equivalent  evaporation  from  and  at  212°  per 

pound  of  coal  as  fired 8.29     Ib. 

49.  Equivalent  evaporation  from  and  at  212°  per 

pound  of  dry  coal 8.65     Ib. 

50.  Equivalent  evaporation  from  and  at  212°  per 

pound  of  combustible 9.62     Ib. 

EFFICIENCY 

51.  Efficiency  of  boiler  (heat  absorbed  per  pound 

of  combustible  burned  on  the  grate  divided 
by  the  heating  value  of  1  Ib.  of  com- 
bustible)    69.5  per  cent 

52.  Efficiency  of  boiler  and  grate  (heat  absorbed 

per  pound  of  dry  coal  fired,  divided  by  the 

heating  value  of  1  Ib.  of  dry  coal) 67.9      per  cent. 


340  STEAM  BOILERS 

277.  Calculation  of  Results.— 

Item  6.  —  The  barometer  pressure  in  pounds  per  square  inch, 
which  represents  the  pressure  of  the  atmosphere,  equals 
28.5  X.  4908  =  14  Ib.  per  sq.  in. 

Item  8.  —  The  absolute  steam  pressure  is  found  by  adding  the 
atmospheric  pressure  to  the  pressure  shown  by  the  gage,  or 
14  +  95.7  =  109.7  Ib.  per  sq.  in. 

Item  21.  —  The  combustible  part  of  the  coal  is  made  up  of  ail  the 
parts  that  will  burn;  therefore,  the  ash  and  moisture  are 
excluded.  In  a  pound  of  dry  coal  there  is  less  than  a  pound 
of  combustible  matter,  therefore  the  heating  value  per  pound 
of  combustible  is  greater  than  the  heating  value  per  pound 
of  dry  coal.  In  this  case  the  combustible  matter  is 

60+28.22  ^88.22 

60+28.22+7.58~95.80 

=  92.1  per  cent  of  the  weight  of  the  dry  coal.     Therefore, 

12300 
the  heating  value  of  the  combustible  is  —      ^-  =  13,360  B.t.u. 


If  the  heating  value  of  the  coal  had  been  given  as  11,800 
B.t.u.  per  pound  of  wet  coal  or  as  fired,  the  per  cent  of 
moisture  would  have  been  added  to  the  denominator,  or 


22 

combustible  matter  =       -i--  =  88.22  per  cent 


of  the  wet  coal,  and  the  heating  value  of  the  combustible 

1  1800 
would  be  -^Q-^5  —  13,375  B.t.u.  per  pound. 

oo.  ZZ 

Item  23.  —  If  the  coal  fired  had  been  dry,  it  would  have  weighed 
only  100  —4.2  =  95.8  per  cent  as  much  as  when  wet,  or  when 
containing  4.2  per  cent  of  moisture.  Therefore,  the  weight 

of  dry  coal  fired  is  equal  to  Item  22  X  (—    ~f7Trr      ~)  — 


32,200  X  =  32,200  X.  958  =30850  Ib. 


Item  25.  —  In  firing  a  boiler  there  is  always  more  or  less  loss  of 
combustible  material  through  the  grates  in  the  form  of 
small  particles  of  coal  and  coke.  According  to  the  analysis 
of  the  coal,  the  pure  ash  alone  should  weigh  (Item  22  X 

,   or  32,200  X.  0758  =2440  Ib.     The   ash   actually 
taken  from  the  ash  pit  weighed  2870  Ib.  (Item  24)  ;  therefore 


BOILER  TESTING  341 


it  must  have  contained,  Item  24  —  (Item  22  X  -  —  r^  —  )  , 

luu     / 

2870  -  (32,200  X  .0758)  -2870  -2440  =430  Ib.  of  combustible 

430 
material,  which  is  ^-T.  —  15  per  cent  of  the   refuse  in  the 


or 


ash  pit. 

Item  26.  —  The  combustible  material  burned  on  the  grate  is  the 
total  amount  of  dry  coal  fired,  less  the  amount  of  ash  and 
combustible  material  in  the  ash  pit,  the  weight  of  dry  coal 
being  taken  because  the  ashes  are  also  dry,  or  Item  23  — 
Item  24-30,850  -2870-27,980  Ib.  of  combustible  material 
actually  burned. 

Item  27.—  -Item  23  -Item  2 
-30,850-20-1543. 

Item  28.—  -Item    27  -Item    3 
-1543-60-25.7 

Item  29.—  -Item  26  -Item  2 
-27,980-20-1399. 

Item  30.—  -Item  29  -Item  3 
=  1399-60  =  23.3. 

Item  35.  —  See  Chapter  VIII  for  method  of  calculating  quality  of 
steam  from  throttling  calorimeter  readings. 

Item  38.  —  All  of  the  moisture  contained  in  the  steam  is  still  in 
the  form  of  water  and  therefore  should  not  be  credited  with 
the  latent  heat  which  would  have  been  required  to  evaporate 
it;  the  moisture,  however,  has  received  enough  heat  to 
raise  it  to  the  boiling-point.  The  total  amount  of  heat 
which  is  given  to  the  feed  water  by  the  boiler  is  the  heat  in 
the  dry  steam  plus  the  heat  in  the  moisture  which  the  steam 
contains.  The  heat  contained  in  the  dry  steam  is  found  by 
multiplying  the  total  weight  of  feed  water  by  the  quality  or 

Item  37  X—  Tnn~^  an(^  ^his  quantity  by  the  number  of  heat 
1UU 

units  given  to  1  Ib.  of  dry  steam.  The  total  heat  contained 
in  the  moisture  in  the  steam  is  found  by  multiplying  the  total 
weight  of  feed  water  by  the  percentage  of  moisture,  stated  as 

,     .      ,  /100-Item  35\ 
a  decimal  I  —    ~Tr\f\  —  ""*]  and  multiplying  this  quantity  by 

the  heat  added  to  the  feed  water  inside  the  boiler,  or  the 
heat  of  the  liquid  (h)  minus  (Item  12-32°). 
Thus  the  number  of  pounds  of  dry  steam  formed  is 

Item  37  X  -  =  250,500  X  .982  =  245,990  Ib. 


342  STEAM  BOILERS 

The  amount  of  heat  given  to  each  pound  of  dry  steam  by  the 
boiler  is 

H-(t  -32)  =1183.9  -  (172  -32) 
=  1183.9-140 
=  1043.9  B.t.u. 

in  which  H  is  the  total  heat  above  32°  of  1  Ib.  of  dry  steam, 
and  t  is  the  temperature  of  the  feed  water. 
Therefore,  the  total  heat  given  the  dry  steam  by  the  boiler  is 

245,990  X  1043.9  =256,788,960  B.t.u. 
The  per  cent  of  moisture  in  the  steam  is 
100  -Item  35  = 
100-98.2  =  1.8  per  cent 

The  total  weight  of  moisture  contained  in  the  steam  is 
Item  37  X.  018  = 
250,500  X.  018  =4509  Ib. 

The  amount  of  heat  given  to  1  Ib.  of  this  moisture  by  the 
boiler  is 

h  -(t-32)  =305  -140 

=  165   B.t.u. 

in  which  h  is  the  heat  of  the  liquid  above  32°. 
Therefore,  the  total  heat  given  the  moisture  by  the  boiler  is 

4509X165  =  743,985  B.t.u. 

The  total  amount  of  heat  given  to  the  feed  water  by  the 
boiler  is  the  sum  of  the  heat  given  to  the  dry  steam  and  that 
given  to  the  moisture  or, 

256,788,960  +  743,985=257,532,945 

The  weight  of  dry  steam  which  this  amount  of  heat  would 
form  is 

257,532,945  +  {H-(t  -32)  (  = 
257,532,945  -5-1183.9  -  (172  -32) 
257,532,945  4-  1043.9  =246,700  Ib.  (nearly) 
The  result  given  is  Item  38. 

The  above  result  may  be  obtained  by  the  use  of  the  following 
formula: 


In  which  W  =  weight  of  water  fed  to   the   boiler    =   Item  37 
_Item  35 

"  :        100 

100-Item  35 


BOILER  TESTING  343 

h  =heat  of  the  liquid  of   1  Ib.  of  steam  above  32° 
H  =  total  heat  of  1  Ib.  of  steam  above  32° 
Thus, 

Item  38  -  250,500  {  .982  +  .018 

=  250,500{.982  +  (.018X.158)} 

-  250,500  X.  98,484-246,700  Ib.  (nearly) 

Item  39.  —  The  factor  of  evaporation  and  its  use  has  been  ex- 
plained in  Chapter  VIII.  The  factor  of  evaporation  is 
always  the  quantity  of  heat  supplied  to  the  water  in  making 
one  pound  of  dry  steam  divided  by  the  latent  heat  of  one 
pound  of  steam  at  212°  or  14.7  Ib.  per  sq.  in.,  which  is 
965.8.  The  heat  supplied  to  the  water  in  making  1  Ib.  of 
steam  is  equal  to  the  total  heat  of  1  Ib.  of  steam  at  the 
boiler  pressure  minus  the  quantity  of  heat  already  in  the 
feed  water  when  it  enters  the  boiler, 

or 

Factor  of  evaporation  =  —  n-*e~5 


in  which  t  is  the  temperature  of  the  feed  water. 
H-(t-32l  =  1183.9-(172-32)  = 

965.8  965.8 

Item  40.  —  It  is  often  desirable  to  compare  the  performance  of  two 
boilers  which  are  generating  steam  under  different  pres- 
sures.    In  order  to  do  this  it  is  necessary  to  reduce  the 
evaporation  to   a  common  pressure;    in  other  words,    to 
change  the  amount  of  water  actually  evaporated   into  the 
amount  that  would  be  evaporated  at  the  common  pressure, 
zero  Ib.  per  sq.  in.  by  the  gage,  or  atmospheric  pressure. 
This  is  done  by  multiplying  the  actual  number  of  pounds  of 
dry  steam  generated  by  the  factor  of  evaporation,  or 
Item  38  X  Item  39 
246,700X1.081=267,000. 
Item  41.  —  Item  41  =  Item  38-  Item  2 

=  246,700-20  =  12,335. 
Item  42.—  Item  42  =  Item  40  -Item  2 

=  267,000-20=13,350. 
Item  43.  —   Item  43  =  Item  42  -Item  4 

=  13,350-2500  =  5.34. 

Item  44.  —  The  horse-power  of  a  boiler  is  the  total  equivalent 
evaporation  per  hour  divided  by  34.5 
Item  44  =  Item  42-34.5  = 


344  STEAM  BOILERS 

13,3504-34.5-387. 
Item  45. — Item  45  =  Item  4  4-  number  of  square  feet  of  heating 

surface  alloted  to  each  horse-power. 
Item  46.— Item  46  =  Item  44  4-  Item  45 

-387 ^-250  =  154. 8  per  cent. 

Item  46. — The  items  numbered  from  47  to  52  inclusive  aie  most 
useful  in  comparing  the  performance  of  boileis.  If  the  per- 
formance of  two  boilers  are  compared  upon  the  basis  of  the 
number  of  pounds  of  water  evaporated  per  pound  of  coal 
as  fired,  the  amounts  of  ash  and  moisture  in  the  coal  used 
affect  the  results. 
Item  47  =  Item  37  4- Item  22 

-250,500-32,200-7.78. 

Item  48. — Item  47  is  not  suitable  as  a  basis  for  comparing  the 
performances  of  two  boilers  working  under  different  pres- 
sures or  generating  steam  of  different  qualities.     Item  48 
corrects  for  both  of  these  things. 
Item  48  =  Item  40  4-  Item  22 

=  267,0004-32,200-8.29. 

Item  49. — Corrects  not  only  for  the  pressure  and  quality  but  also 
for  the  moisture  in  the  coal.     It  is  equal  to 
Item  49    -  Item  40  4-  Item  23 

-267,0004-30,850-8.65. 

Item  50. — Corrects  for  the  pressure  and  quality  of  the  steam,  for 
the  ash  and  moisture  in  the  coal  and  also  for  the  amount  of 
combustible  material  dropping  through  the  grates.  It  is, 
therefore,  a  fair  basis  of  comparison  for  boilers  alone,  con- 
sidered separately  from  their  furnaces. 
Item  50  -  Item  40  4-  Item  26 

=  267,000-4-27,780-9.61. 
Item  51. —  Item  51=  Item  50x965.8  4- 1  tern  21 

=  9.62X965.8  4- 13,360  =  .695  =  69.5  per  cent 
I tern  52.—  Item  52-  Item  49X965.8  4- Item  20 

=  8.65X965.84- 12,300  =  . 679-67.9  per 

cent 

278.  Forms  and  Data. — In  the  following  pages  are  shown  a  set 
of  convenient  forms  for  recording  the  data  taken  duiing  a 
boiler  test.  These  forms  are  shown  filled  in  with  the  data  from  a 
different  boiler  test  and  show  the  manner  in  which  it  may  be 
recorded.  On  account  of  the  small  space  in  the  blank  form,  the 
coal  sheet  does  not  show  the  time  of  firing  nor  the  amount 


BOILER  TESTING  345 

of  coal  fired  each  time,  but  simply  the  amount  of  coal  delivered 
in  front  of  the  boiler  each  time.  In  carrying  out  a  test  it  would 
be  better  to  use  several  sheets  of  paper,  ruled  like  the  coal  sheet, 
and  record  on  them  the  amount  of  coal  left  in  the  wheelbarrow 
after  each  firing.  Errors  in  the  observations  may  then  be 
detected. 

The  analysis  of  the  coal  used  during  this  test  was  as  follows: 

Fixed  carbon 54. 10  per  cent 

Volatile  matter 24. 21  per  cent 

Moisture 12. 19  per  cent 

Ash 9 . 50  per  cent 

Heating  value  per  pound  of  dry  coal,  13,530  B.t.u. 

On  account  of  the  irregular  times  at  which  the  furnaces  are 
fired,  the  weights  of  coal  cannot  usually  be  taken  at  regular  inter- 
vals, but  this  should  be  done  whenever  possible. 

The  amount  of  feed  water  used  by  the  boiler  will  also  vary 
from  hour  to  hour.  It  should  be  weighed  in  equal  portions,  the 
weighing  tanks  being  filled  to  a  certain  height  and  then  emptied 
into  the  feed  tank.  If  the  water  is  weighed  in  equal  portions, 
the  time  of  weighing  will  ordinarily  vary. 

The  readings  for  the  calorimeter  should  be  taken  at  regular 
intervals  of  about  20  minutes  throughout  the  test,  all  the  read- 
ings being  taken  at  as  near  the  same  time  as  possible.  In  calcu- 
lating the  quality  of  steam  from  the  calorimeter  readings,  it  is  not 
sufficient  to  take  the  average  of  the  readings  and  calculate  the 
quality  from  these  average  readings.  The  quality  should  be 
calculated  separately  from  each  set  of  readings,  and  the  average 
of  the  qualities  used  in  the  report  of  the  test.  It  is  necessary  to 
read  the  barometer  only  two  or  three  times  during  a  test  as  it 
varies  but  little  during  a  day. 

The  readings  of  draft  gages,  stack  temperature,  and  temper- 
ature of  feed  water  should  be  taken  every  20  minutes  if  possible. 
The  flue  gas  should  also  be  analyzed  every  20  or  30  minutes,  and 
the  average  of  all  the  analyses  recorded  in  the  report  of  the  test. 
The  following  data  is  not  shown  in  the  data  sheets  and  is 
given  here  in  order  to  make  the  set  of  data  complete. 

Type  of  boiler  =  Scotch  Marine 

Kind  of  furnace  =  Morison  Suspension 

Duration  of  test  =  10  hours 

Grate  surf  ace  =40  sq.  ft. 

Water  heating  surface  =  1470  sq.  ft. 

Builders'  rated  horse-power  =  200 


346 


STEAM  BOILERS 

LOG  OF  BOILER  TRIAL  No.  2 


Made 
Date 
Boile 

at   

Rv... 

r  No                                        .                          Fireman 

Coal  Sheet 

Time 

Coal 
delivered 
to  scales, 
pounds 

Coal  on 
scales 
after  each 
firing, 
pounds 

Coal 
fired 
each 
time, 
pounds 

Fuel 

7:00 

400 

0 

400 

Moist  coal  consumed,  Ib. 

7:52 

600 

0 

600 

Wood  consumed,  Ib. 

8:43 
9:41 

600 

0 

600 

Coal  equivalent  of  wood  =(woodX4),  Ib. 

600 

0 

600 

10:30 

600 

0 

600 

11:20 

800 

0 

800 

12:15 

800 

0 

800 

Description  of  fuel. 

1:00 

600 

0 

600 

Commercial  name,  Washed  No.  4. 

1:45 

600 

0 

600 

Where  mined,  Huron,  III. 

2:36 

600 

0 

600 

Size  No.  4. 

3:20 

600 

0 

600 

Kind,  bituminous. 

4:00 

600 

0 

600 

Appearance  of  coal. 

4:45 

600 

0 

600 

Record  of  cleaning  fires. 

5:50 

460 

0 

460 

Time                               Ash,  Ib. 

12:20                                  295 

12:35                                    119 

6:00                                  531 

Total  Dry  Ash,  945  Ib. 

BOILER  TESTING 

LOG  OF  BOILER  TRIAL  No.  2 


347 


Made 
Date. 
Boiler 

at  

By. 
Fire 

ter  Sheet 

No 

man          .  .    . 

Feed  Wa 

Time 

Water 
delivered  to 
feed  tank, 
pounds 

Temp,  of 
water  in 
tank 

Time 

Water 
delivered  to 
feed  tank, 
pounds 

Temp,  of 
water  in 
tank 

Remarks 

7:00 

7855 

196 

Test  began  at  7:00 
A.  M.;  date,  Mar. 
26.  Test  closed 
at  6:00  P.  M.; 
date,  Mar.  26. 

8:30 
9:00 
9:40 
10:00 

3169 

197 

3244 

196 

2567 

196 

5845 

196 

11:00 

5638 

198 

12:01 

6339 

199 

1:00 

6449 

197 

2:03 

9076 

198 

3:45 

3312 

200 

4:03 

3275 

200 

4:52 

2600 

195 

5:04 

4290 

180 

348 


STEAM  BOILERS 


LOG  OF  BOILER  TRIAL  No  2 


Made 
Date. 
Boiler 

it 

By 

Fir 

No  

sman. 

Time 

Pressures 

Temperatures 

Height 
of  water 
in  gage 
glass 

Remarks 

i! 

|o 

Draft  j?age 

Li 

Boiler 
room 

External 
Air 

1 
§ 

E 

Feed  water 

£ 

! 

GO 

7:00 

115 

1.2 

29.2 

86 

15 

196 

Test  began  at 
7:00  A.  M;  date, 
Mar.  26.  Test 
closed  at  6:00 
P.M.;  date,  Mar. 
26. 

8:00 

113 

1.8 

84 

16 

197 

9:00 

120 

1.7 

87 

15 

545 

196 

10:00 

110 

1.6 

86 

17 

572 

196 

11:00 

100 

1.8 

90 

20 

590 

198 

12:00 

108 

1.8 

29.1 

91 

19 

626 

199 

1:00 

101 

1.7 

92 

20 

617 

197 

2:00 
3:00 

112 

1.6 

92 

21 

550 

198 

101 

1.7 

29.2 

90 

19 

635 

197 

4:00 

100 

1.6 

90 

19 

671 

200 

5:00 

110 

1.6 



93 

19 

586 

195 

i 

6:00 

109 

1.4 

29.2 

90 

16 

180 

BOILER  TESTING 

LOG  OF  BOILER  TRIAL  No.  2 


349 


Made 
Date. 

at 

By. 
Fire 

Boiler  No  

man.  . 

Time 

Calorimeter 

Draft,  In.  of  water 

Height 
of  water 
in  tank 

Height 
of  water 
in  gage 
glass 

Remarks 

Gage  pressure 

Calorimeter  tem- 
perature, or  steam 
discharge 

Calorimeter  pres- 
sure or  water 
separated 

Between  damper 
and  boiler 

1 

q 

i—  i 

i 

jq 
% 

a 
i—  i 

7:00 
8:00 

115 

276 

1.50 

1.2 

.20 

5.5 

113 

280 

1.55 

1.8 

.42 

5.3 

9:00 
10:00 
11:00 

120 

281 

1.55 

1.7 

.40 

5.8 

110 

279 

1.50 

1.6 

.36 



6.0 

•  100 

277 

1.50 

1  8 

.40 

5.4 

12:00 

108 

280 

1.45 

1.8 

.38 

5.1 

1:00 

101 

276 

1.45 

1.7 

.40 

5.7 

2:00 

112 

279 

1.55 

1.6 

.40 

5.8 

3:00 

101 

274 

1.40 

1.7 

.32 

5.5 

4:00 
5:00 
6:00 

100 

276 

1.35 

1.6 

.40 

5.3 

110 

280 

1.50 

1.6 

40 

5.2 

109 

278 

1.55 

1.4 

40 

5.5 



350 


STEAM  BOILERS 


LOG  OF  BOILER  TRIAL  No.  2 


Made  a 
Date.  . 
Boiler  J 

Rv 

Jo 

I 

ue  Gas  Sh 

Fl 

eet 

Time 

CO2 

02 

CO 

Total 

Remarks 

7:20 

7.20 

11.40 

0.2 

8:15 

6.30 

13.70 

0.3 

9:15 

8.55 

10.90 

0.1 

10:10 

6.80 

12.60 

0.5 

11:20 

6.20 

12.20 

0.8 

12:15 

7.20 

11.40 

0.6 

1:20 

6.70 

12.20 

0.6 

2:15 

5.70 

10.40 

1.4 

3.15 

6.25 

9.85 

1.1 

4:20 
5:25 

7.20 

11.80 

0.7 

8.00 

6.50 

1.5 





j 

INDEX 


Absolute  zero,  90 

Actual  and  equivalent  evaporation, 
115 

Air  heaters,  284 

Air  required  for  combustion,  152 

Allowance  for  feed  water  tempera- 
ture, 108 

Alternate  method  of  firing,  162 

Analysis  of  flue  gas,  157 
reagents  used  in,  160 

Area,  disengagement,  1 
of  grate,  2 

Ash,  weighing,  336 

Atlas  water-tube  boiler,  27 

Atmospheric  pressure,  97 

Atomic  weight,  149 

Atoms  and  molecules,  148 


B 


Babcock    and    Wilcox 

boiler,  21 

Back  connections,  207 
Banking  fires,  330 
Baragwanath  heater,  314 
Barometers,  97 
Blisters,  328 
Blow  off,  bottom,  240 

connections,  208 

surface,  240 
Blowing  out,  330 
Bolts,  stay,  55 
Boiler,  Atlas,  27 

Babcock  and  Wilcox,  21 

Cahall,  32 

cleaning,  297 

cleaners,  299 

cylindrical,  3 

Edge  Moor,  25 

Galloway,  7 

29 


Figures  refer  to  pages. 

Boiler,   fire-tube,  7 

heads,  58 

horse-power  of,  39,  136 

Lancashire,  6 

materials  of,  1 

Murray,  24 

rust,  33 

settings  for,  195 

shell,  1 

Stirling,  28 

supports  for,  201 

vertical  water  tube,  31 

Vogt,  29 

Wickes,  31 
Boiler  testing,  333 

alternate  method,  337 

calculation  of  results,  340 

forms  and  data,  340 

method  of,  333 

observations  for,  333 

results,  337 

starting  and  stopping,  336 

standard  method  of,  336 
Boilers,  care  of,  326 

classes  of,  2 

Cornish,  4 

cutting  in,  329 

defects  in,  319 

disuse  of,  331 

dry-back,  17 

fire  tube,  3 

flue,  3 

inspection  and  care  of,  319 

locomotive,  11 

Manning,  19 

portable,  11 

Scotch  marine,  14 

vertical  fire  tube,  18 

water  tube,  3,  21 
Bottom  blow-off,  240 
Bridge  wall,  202 

split,  203 
351 


water-tube 


352 


INDEX 


Brickwork,  leaks  in,  331 
Buck  stays,  212 
Burke  furnace,  206 
Burnt  plates,  328 


Cahall  water-tube  boiler,  32 
Calorimeters,  steam,  118 
Carbon,  148 

compounds  of,  150 
Carbonates,  288 
Care  of  boilers,  319,  326 
Caustic  potash,  160 
Centigrade  thermometer,  78 
Chain  grate  stoker,  174,  189 
Chemical  definitions,  148 
Chicago  setting,  204 
Chimneys,  271 

for  oil  fuel,  275 

steel,  275 

concrete,  277 

brick,  277 
Chlorides,  290 
Circulation,  93 
Classes  of  boilers,  2 
Cleaners,  mechanical,  299 
Cleaning  boilers,  297,  331 
Closed  stoke  hole,  312 
Coal,  138 

anthracite,  142 

bituminous,  141 

cannel,  141 

caking,  141 

sampling,  334 

semi-anthracite,  142 

semi-bituminous,  141 

sizes  of,  142 

weighing,  334 
Coefficient  of  expansion,  87 
Coking  method  of  firing,  161 
Combustion,  147 

air  required  for,  152 

of  fuel,  151 

smokeless,  179 
Comparison  of  boilers,  35 
Compounds  of  carbon  and  oxygen, 

150 
Convection,  91,  92 


Cornish  boilers,  4 
Corrosion,  328 
Corrugated  flues,  45 
Covering,  328 
Cracks,  328 
Cuprous  chloride,  160 
Cutting  in  boilers,  329 
Cycle  of  steam  plant,  84 
Cylindrical  boiler,  3 

D 

Dampers,  255 
Damper  regulator,  327 
Defective  fittings,  325 
Defects  in  boilers,  319 
Density  of  steam,  108 

of  superheated  steam,  131 
Diagonal  stays,  59 
Disengagement  area,  1 

surface,  96 
Dished  heads,  64 
Disuse  of  boilers,  331 
Draft,  271 

artificial,  279 

mechanical,  280 

forced,  281 

induced,  282 
Dry-back  boiler,  17 
Dry  pipes,  243 
Duplex  pumps,  259 
Dutch  oven  furnace,  203 


E 


Economizers,  284,  303 

Edge  Moor  water-tube  boiler,  25 

Effects  of  heat,  87 

impurities,  290 
Energy,  74 

of  fuels,  76 

Equivalent  evaporation,  115,  132 
Erecting  pipe,  225 
Evaporation,  101 

actual  and  equivalent,  115 

equivalent,  132 

factor  of,  134 

temperature  of,  104 
Exhaust  steam  heaters,  66 


INDEX 


353 


Expanders,  tube,  66 
Expansion  bends,  224 

joints,  223 

of  gases,  89 

of  liquids,  88 

of  solids,  87 

of  water  into  steam,  108 


Factor  of  evaporation,  134 
Feeding,  330 
Feed  pumps,  256,  327 
Feed  water,  281 
heaters,  303 

Baragwanath,  313 
closed,  312 
Cochrane,  306 
exhaust  steam,  304 
Goubert,  315 
Hoppes,  311 
induced,  309 
live  steam,  317 
National,  315 
open,  306 
Otis,  313 
Pittsburgh,  310 
steam  tube,  313 
heating,  331 
impurities  in,  288 
temperature  of,  108,  312 
treatment  of,  295 
Fires,  banking,  330 
Fire-tube  boilers,  3,  7 
Firing,  329 

methods  of,  161 
rapid,  330 
rules  for,  163 
tools,  2 

Fittings,  defective,  325 
Flexible  stay  bolt,  57 
Flue  boilers,  3 

strength  of  furnace,  49 
gas,  155 

analysis,  157 
Flues,  corrugated,  45 
Morison,  45 
Fox,  45 
Foaming,  330 


Formation  of  steam,  95 

Forms  for  boiler  testing,  316,  338 

Foundations,  195 

Fox  corrugated  flue,  45 

Fractures,  lap,  323 

Fuels,  classification  of,  137 

energy  of,  76 

heating  value  of,  143 
Furnace,  Burke,  206 

down  draft,  192 

hand  fired,  190 

strength  of  flue,  49 

types  of,  188 
Fusible  plugs,  328 
Future  of  superheated  steam,  132 

G 

Gage  cocks,  239 

pressure,  98,  327 

steam,  236 

water,  237 
Galloway  boiler,  7 
Galvanic  action,  328 
Gases,  expansion  of,  89 
Goubert  heater,  315 
Girder  stays,  60 
Grate  bars,  216 

shaking,  215 

surface,  2 
Green  walls,  328 
Grooving,  320 
Gusset  stays,  63 

H 

Hand  holes,  68 
Hand-fired  furnaces,  190 
Hammer  test,  324 
Heads,  dished,  64 

of  boilers,  58 
Heat,  75 

cycle  of  steam  plant,  84 

equivalent,  84 

of  the  liquid,  105 

sensible  and  latent,  74 

transmission  of,  91 
Heating  feed  water,  303,  331 

surface,  2,  40 

value  of  fuels,  143 


354 


INDEX 


Hoppes  heater,  311 

Horse  power,  74 

calculation  of,  39 
of  boilers,  136 

Hydraulic  test,  324 


Inclined  grate  stokers,  189 
Injectors,  267,  327 
Impurities  in  feed  water,  288 
Incrustation,  328 
Induced  draft,  283 

heaters,  309 

Inspection  of  boilers,  319 
Interpolation,  109 


Joints,  riveted,  48 

Jones  under-feed  stoker,  170 

K 

Kent  wing  wall  setting,  213 
L 

Lancashire  boiler,  6 
Lap  fractures,  323 
Latent  heat,  76,  106 
Leaks  in  brickwork,  331 
Lignite,  140 

Liquids,  expansion  of,  88 
Locomotive  boiler,  11 
Low  water,  327 

M 

Manholes,  68 
Manning  boiler,  19 
Marine  boiler,  14 
Material  of  boilers,  1 
Measuring  temperatures,  77 
Mechanical  cleaners,  299 

equivalent  of  heat,  84 

stokers,  165 
Method  of  firing,  161 

of  testing  boilers,  333 


Moisture,  331 

Molecular  weight,  149 

Molecules,  148 

Morison  flue,  45 

Mud,  291 

Murphy  stoker,  168 

Murray  water-tube  boiler,  24 

N 

National  heater,  315 
O 

Oil  burners,  177 

burning,  176 
Open  heaters,  306 
Otis  heater,  313 
Oxygen,  147 


Patches,  321 
Peat,  137 
Petroleum,  142 
Pipe,  covering,  228 

determining  size  of,  221 

erecting,  225 

kinds  of,  219 
Pittsburgh  heater,  310 
Portable  boilers,  11 
Power,  74 

Power  plant,  cycle  of,  84 
Pressure,  103 

absolute,  98 

atmospheric,  97 

gage,  98 

Prevention  of  smoke,  165 
Priming,  291 

Principles  of  smokeless  combustion, 
180 

of  staying,  55 
Pumps,  duplex,  259 

feed,  256,  327 
Pyrogallol,  160 
Pyrometers,  79 

Q 

Quality  of  steam,  117 


INDEX 


355 


R 


Radial  stays,  63 

Radiation,  91 

Rapid  firing,  330 

Riveted  joints,  proportions  of,  48 

Riveting,  50 

Roney  stoker,  167 

Rules  for  hand  firing,  163 

Rust  water-tube  boiler,  33 


Safety  plugs,  240 

stay  bolt,  56 

values,  232,  326 
Sampling  coal,  334 
Saturated  steam,  102 
Scale,  287 

preventing,  291 
Scotch  dry-back  boiler,  17 

marine  boiler,  14 
Screwed  stay  repairs,  323 
Setting,  boiler,  195 

Chicago,  204 

for  fire-tube  boilers,  195 

Kent  wing  wall,  213 

steel,  215 

tubes,  64 

water-tube  boiler,  212 

Wooley  smokeless,  215 
Sensible  heat,  76 
Separating  calorimeter,  118 
Shaking  grates,  215 
Shell,  1 

strength  of,  46 
Side  feed  stokers,  190 
Sling  stays,  62 
Smoke,  causes  of,  182 

means  of  preventing,  183 

prevention,  165 
Smokeless  combustion  of  coal,  179 

principles  of,  180 
Split  bridge  wall,  203 
Spreading  method  of  firing,  163 
Starting  engines,  329 
Stay  bolts,  55 

flexible,  57 

safety,  56 

repairs,  323 


Staying,  principles  of,  55 
Stays,  diagonal,  59 

girder,  60 

gusset,  63 

radial,  63 

sling,  62 

through,  64 

tube,  63 
Steam,  calorimeters,  118 

density  of,  108 

formation  of,  95 

gage,  236 

heat  of  the  liquid  of,  105 

jets,  279 

latent  heat  of,  106 

quality  of,  117 

saturated,  102 

space,  1,  96 

specific  volume  of,  108 

superheated,  129 

tables,  103 

total  heat  of,  107 

tube  heaters,  313 

wet,  115 

Steel  settings,  215 
Stirling  water-tube  boiler,  28 
Stokers,  advantages  and  disadvan- 
tages of,  175 

chain  grate,  174,  189 

inclined  with  front  feed,  189 

Jones  under-feed,  170 

mechanical,  165 

Murphy,  168 

Roney,  167 

Taylor,  172 

under-feed,  190 

Wilkinson,  166 

with  side  feed,  190 
Strength  of  furnace  flue,  49 

of  shell,  46 
Sulphates,  289 
Superheated  steam,  129 

density  of,  131 

future  of,  132 
Superheating  surface,  2 
Superheaters,  131 

Babcock  and  Wilcox,  248 

Foster,  247 
Heine,  252 


356 


INDEX 


Superheaters,  Schmidt,  253 

Stirling,  251 

Supports  for  boilers,  201 
Surface,  blow-off,  240 

disengagement,  96 

grate,  2 

heating,  2 

superheating,  2 


Unit  of  heat,  83 


Vacuum,  98 

Valves,  safety,  232,  326 

Vertical  fire-tube  boilers,  18 

water-tube  boilers,  31 
Vogt  water-tube  boiler,  29 


Taylor  stoker,  172 
Temperature,  77 

of  evaporation,  104 
of  feed  water,  312 

allowance,  108 
Test  of  boilers,  333 

alternate  method,  337 
calculating  results,  340 
forms  and  data,  344 
hammer,  324 
hydraulic,  324 
method  of,  333 
results  of,  337 
standard  method,  336 
starting  and  stopping,  336 

Thermometer  scales,  77 

Thermometers,  comparison  of,  78 

Throttling  calorimeter,  121 

Through  stays,  64 

Tools,  firing,  2 

Total  heat  of  steam,  107 

Transmission  of  heat,  91 

Treatment  of  feed  water,  295 

Tube  expanders,  66 
setting,  64 

Tubes,  stay,  63 

Turbine  cleaners,  300 

Types  of  boilers,  comparison,  35 
of  furnaces,  188 


U 


W 

Walls,  green,  328 
Water  columns,  239 

gages,  237 

level,  327 

line,  1 

weighing,  335 
Water-tube  boilers,  3,  21 

Atlas,  27 

Cahall,  32 

Edge  Moor,  25 

Murray,  24 

Rust,  33 

Stirling,  28 

vertical,  31 

Vogt,  29 

Wickes,  31 

settings  for,  212 
Water-tube  heaters,  315 
Weighing  coal,  334 

water,  335 
Wet  steam,  115 
Wickes  water-tube  boiler,  31 
Wing  wall  setting,  Kent,  213 
Wilkinson  stoker,  166 
Wood,  137 

Wooley  smokeless  setting,  215 
Work,  73 


Under-feed  stokers,  190 


Zero,  absolute,  90 


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